Update prometheus.py

[HimanshuGitCode]

Key Improvements:

1. Session Handling Encapsulated: A new helper function get_or_set_session_id manages session handling to improve code readability and reusability.
2. Agent Exclusion Using Regex: Replaced any with a regex match, improving speed and scalability as the number of agents grows.
3. Improved Error Handling: Added try-except blocks around the middleware's main logic to catch any unexpected errors and log them.
4. Logging for Errors: Error logging is added to help diagnose any issues during request processing.
5. Referred to request.url.path: Corrected request.get('path') to request.url.path for accessing the request's path.