When you've never built `helm-chart` documentation package locally. the intersphinx repository is missing for it and it cannot be downloaded as the helm-chart package is never published as package (I guess) . 

This fails for example our command to build provider's documentation when you release providers:

```
cd "${AIRFLOW_REPO_ROOT}"
./breeze build-docs -- \
  --for-production \
  --package-filter apache-airflow-providers \
  --package-filter 'apache-airflow-providers-*'
```

Adding `--package-filter 'helm-chart'` helps, but it also builds the helm-chart documentation which is undesired in this case (and it causes the docs-building for most providers to fail the first pass, until the `helm-chart` documentation is built

Possibly there is a way to get rid of that dependency ? 

The error you get:

```
apache-airflow-providers                                     Traceback (most recent call last):
apache-airflow-providers                                       File "/usr/local/lib/python3.6/site-packages/sphinx/cmd/build.py", line 279, in build_main
apache-airflow-providers                                         args.tags, args.verbosity, args.jobs, args.keep_going)
apache-airflow-providers                                       File "/usr/local/lib/python3.6/site-packages/sphinx/application.py", line 278, in __init__
apache-airflow-providers                                         self._init_builder()
apache-airflow-providers                                       File "/usr/local/lib/python3.6/site-packages/sphinx/application.py", line 337, in _init_builder
apache-airflow-providers                                         self.events.emit('builder-inited')
apache-airflow-providers                                       File "/usr/local/lib/python3.6/site-packages/sphinx/events.py", line 110, in emit
apache-airflow-providers                                         results.append(listener.handler(self.app, *args))
apache-airflow-providers                                       File "/usr/local/lib/python3.6/site-packages/sphinx/ext/intersphinx.py", line 238, in load_mappings
apache-airflow-providers                                         updated = 
apache-airflow-providers                                       File "/usr/local/lib/python3.6/site-packages/sphinx/ext/intersphinx.py", line 238, in <listcomp>
apache-airflow-providers                                         updated = 
apache-airflow-providers                                       File "/usr/local/lib/python3.6/concurrent/futures/_base.py", line 425, in result
apache-airflow-providers                                         return self.__get_result()
apache-airflow-providers                                       File "/usr/local/lib/python3.6/concurrent/futures/_base.py", line 384, in __get_result
apache-airflow-providers                                         raise self._exception
apache-airflow-providers                                       File "/usr/local/lib/python3.6/concurrent/futures/thread.py", line 56, in run
apache-airflow-providers                                         result = self.fn(*self.args, **self.kwargs)
apache-airflow-providers                                       File "/usr/local/lib/python3.6/site-packages/sphinx/ext/intersphinx.py", line 224, in fetch_inventory_group
apache-airflow-providers                                         "with the following issues:") + "\n" + issues)
apache-airflow-providers                                       File "/usr/local/lib/python3.6/logging/__init__.py", line 1642, in warning
apache-airflow-providers                                         self.log(WARNING, msg, *args, **kwargs)
apache-airflow-providers                                       File "/usr/local/lib/python3.6/site-packages/sphinx/util/logging.py", line 126, in log
apache-airflow-providers                                         super().log(level, msg, *args, **kwargs)
apache-airflow-providers                                       File "/usr/local/lib/python3.6/logging/__init__.py", line 1674, in log
apache-airflow-providers                                         self.logger.log(level, msg, *args, **kwargs)
apache-airflow-providers                                       File "/usr/local/lib/python3.6/logging/__init__.py", line 1374, in log
apache-airflow-providers                                         self._log(level, msg, args, **kwargs)
apache-airflow-providers                                       File "/usr/local/lib/python3.6/logging/__init__.py", line 1444, in _log
apache-airflow-providers                                         self.handle(record)
apache-airflow-providers                                       File "/usr/local/lib/python3.6/logging/__init__.py", line 1454, in handle
apache-airflow-providers                                         self.callHandlers(record)
apache-airflow-providers                                       File "/usr/local/lib/python3.6/logging/__init__.py", line 1516, in callHandlers
apache-airflow-providers                                         hdlr.handle(record)
apache-airflow-providers                                       File "/usr/local/lib/python3.6/logging/__init__.py", line 861, in handle
apache-airflow-providers                                         rv = self.filter(record)
apache-airflow-providers                                       File "/usr/local/lib/python3.6/logging/__init__.py", line 720, in filter
apache-airflow-providers                                         result = f.filter(record)
apache-airflow-providers                                       File "/usr/local/lib/python3.6/site-packages/sphinx/util/logging.py", line 422, in filter
apache-airflow-providers                                         raise exc
apache-airflow-providers                                     sphinx.errors.SphinxWarning: failed to reach any of the inventories with the following issues:
apache-airflow-providers                                     intersphinx inventory '/opt/airflow/docs/_inventory_cache/helm-chart/objects.inv' not fetchable due to <class 
'FileNotFoundError'>: [Errno 2] No such file or directory: '/opt/airflow/docs/_inventory_cache/helm-chart/objects.inv'
apache-airflow-providers                                     
apache-airflow-providers                                     [91mWarning, treated as error:[39;49;00m
apache-airflow-providers                                     failed to reach any of the inventories with the following issues:
apache-airflow-providers                                     intersphinx inventory '/opt/airflow/docs/_inventory_cache/helm-chart/objects.inv' not fetchable due to <class 
'FileNotFoundError'>: [Errno 2] No such file or directory: '/opt/airflow/docs/_inventory_cache/helm-chart/objects.inv'

```
docs/exts/docs_build/fetch_inventories.py
#
#
import concurrent
import concurrent.futures
import datetime
import os
import shutil
import sys
import traceback
from itertools import repeat
from typing import Iterator, List, Tuple
import requests
import urllib3.exceptions
from requests.adapters import DEFAULT_POOLSIZE
from airflow.utils.helpers import partition
from docs.exts.docs_build.docs_builder import (  
    get_available_providers_packages,
)
from docs.exts.docs_build.third_party_inventories import (  
    THIRD_PARTY_INDEXES,
)
CURRENT_DIR = os.path.dirname(__file__)