Adding fix for incorrect log level bug for versions 2.10.1 & 2.10.3

[Vraj2725]

Issue #, if available:
When using airflow versions 2.9.2 and above customer are unable to see error logs when they set their loglevel to WARNING or above. The root cause is that in subprocess.py, the line self.process_logger.info(line.decode("utf-8")) overrides the log level coming from airflow stream to INFO in subprocess.py.

Description of changes:

• Setting process logger level to DEBUG to emit all logs and setting root logger to customer's log level to respect customer's log level.
• Refactoring entrypoint.py to resolve circular dependency issue and breaking down its logic into different files so all files have single responsibility such as:
  • user_requirements.py: Installing user requirements.
  • execute_command.py: Logic for executing all the subprocesses
  • setup_environment.py: Running the startup script and setting up environment variables

Testing

• Added unit tests for all refactored code.
• Ran log heavy dag on the refactored image code by using local docker.
• Exported environment variable using startup script and verified that it set correctly.

This PR is for V 2.10.1 and 2.10.3. Fix for v2.9.2 has already reached prod.

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