feat: add monitoring signals for plugins

[robrap]

Description:

Adds signals monitoring_support_process_request,
monitoring_support_process_response, and
monitoring_support_process_exception to the
MonitoringSupportMiddleware to enable plugging in
monitoring capabilities.

Merge checklist:

• All reviewers approved
• CI build is green
• Version bumped
• Changelog record added
• Documentation updated (not only docstrings)
• Commits are squashed

Post merge:

• Create a tag
• Check new version is pushed to PyPi after tag-triggered build is
  finished.
• Delete working branch (if not needed anymore)

Author concerns:

I decided to go with monitoring/signals.py vs monitoring/signals/signals.py to clean up the imports when using the signals, especially given the length of the signal names.