Fix issue of replacing the exiting env

[YuchengZhou821]

This pull request updates the logic for retrieving environment variables for containers in OTA/agent/main.py. The method now combines environment variables from both Docker inspect and the .env file, providing a more comprehensive and robust approach.

Improvements to environment variable retrieval:

• The _get_container_env_vars method now fetches environment variables using docker inspect in addition to reading from the .env file, then combines both sources. This ensures that all relevant environment variables are captured, even if they are set at runtime or differ from the .env file. [1] [2]
• Improved error handling for the Docker inspect process, logging warnings if the command fails or times out.
• Updated the method docstring and return value description to reflect the new combined approach. [1] [2]