[x] bug report
[ ] feature request

# Detailed description
`lambda_executor.py` current retrieves the container entrypoint from the docker image via `docker inspect --format="{{ .ContainerConfig.Entrypoint }}" ..`. This is fragile and may be missing depending on how the image in question is built. There is a `config` block _and_ a `containerconfig` block that are mostly the same, but sometimes different depending what built and what version of that thing built the image, for example we are seeing the entrypoint missing on images built with Docker for Mac 2.5.0.1, but not on earlier versions, others using `podman` are noticing the fragility in other projects:

https://github.com/containers/podman/issues/2017

## Expected behavior
entrypoint value is picked up from a validly built container

## Actual behavior
entrypoint is sometimes an empty string, which then for a `provided` lambda executor ends up with a script error trying to execute the handler name.

The simple fix is to change `--format="{{ .ContainerConfig.Entrypoint }}"` to `--format="{{ .Config.Entrypoint }}"` which seems like the more canonical way of getting that value.



┆Issue is synchronized with this [Jira Task](https://localstack.atlassian.net/browse/LOC-54) by [Unito](https://www.unito.io/learn-more)

import os
import re
import sys
import glob
import json
import time
import logging
import threading
import subprocess
import six
import base64
from multiprocessing import Process, Queue
try:
    from shlex import quote as cmd_quote
except ImportError:
    from pipes import quote as cmd_quote  
from localstack import config
from localstack.utils import bootstrap
from localstack.utils.aws import aws_stack
from localstack.utils.common import (
    CaptureOutput, FuncThread, TMP_FILES, short_uid, save_file, rm_rf, in_docker,
    to_str, to_bytes, run, cp_r, json_safe, get_free_tcp_port)
from localstack.services.install import INSTALL_PATH_LOCALSTACK_FAT_JAR
from localstack.utils.aws.dead_letter_queue import lambda_error_to_dead_letter_queue, sqs_error_to_dead_letter_queue
from localstack.utils.cloudwatch.cloudwatch_util import store_cloudwatch_logs, cloudwatched
LAMBDA_EXECUTOR_JAR = INSTALL_PATH_LOCALSTACK_FAT_JAR
LAMBDA_EXECUTOR_CLASS = 'cloud.localstack.LambdaExecutor'