**Description**


It would be great if the metrics we publish in Airflow change to include TAGs for "variable" parts of those (such as dag_id, task_id, pool name) rather than being part of the metrics.

See here: https://airflow.apache.org/docs/1.10.12/metrics.html, https://airflow.readthedocs.io/en/latest/logging-monitoring/metrics.html  - those variable parts should be tags.

We might consider to change those metrics by default in 2.0 and possibly introduce a backport in 1.10.13 to allow people to migrate.


**Use case / motivation**

Having the variable parts of the metrics makes it really difficult to aggregate the metrics. Seems that statsd python library does not support tags, but there are possible solutions by installing extensions:

https://stackoverflow.com/questions/49852654/sending-statsd-metrics-with-tags-from-python-client

**Related Issues**

<!-- Is there currently another issue associated with this? -->

from airflow.callbacks.callback_requests import DagCallbackRequest, SlaCallbackRequest, TaskCallbackRequest
from airflow.callbacks.database_callback_sink import DatabaseCallbackSink
from airflow.callbacks.pipe_callback_sink import PipeCallbackSink
from airflow.dag_processing.manager import DagFileProcessorAgent
from airflow.datasets import Dataset
from airflow.exceptions import AirflowException
from airflow.executors.base_executor import BaseExecutor
from airflow.executors.executor_constants import MOCK_EXECUTOR
from airflow.executors.executor_loader import ExecutorLoader
from airflow.jobs.backfill_job import BackfillJob
from airflow.jobs.base_job import BaseJob
from airflow.jobs.local_task_job import LocalTaskJob
from airflow.jobs.scheduler_job import SchedulerJob
from airflow.models import DAG, DagBag, DagModel, DbCallbackRequest, Pool, TaskInstance
from airflow.models.dagrun import DagRun
from airflow.models.dataset import DatasetDagRunQueue, DatasetEvent, DatasetModel
from airflow.models.serialized_dag import SerializedDagModel
from airflow.models.taskinstance import SimpleTaskInstance, TaskInstanceKey
from airflow.operators.bash import BashOperator
from airflow.operators.empty import EmptyOperator
from airflow.serialization.serialized_objects import SerializedDAG
from airflow.utils import timezone
from airflow.utils.file import list_py_file_paths
from airflow.utils.session import create_session, provide_session
from airflow.utils.state import DagRunState, State, TaskInstanceState
from airflow.utils.types import DagRunType
from tests.listeners import dag_listener
from tests.listeners.test_listeners import get_listener_manager
from tests.models import TEST_DAGS_FOLDER
from tests.test_utils.asserts import assert_queries_count