ARCHBOM-1584: refactor monitoring app

[robrap]

Description:

• Add ADR to explain new app organization.
• Apply new app organization to the monitoring Django app.
• Remove middleware ordering checks. This is not a typical Django feature and it is painful when refactoring.
• Add CachedCustomMonitoringMiddleware, CodeOwnerMonitoringMiddleware, and MonitoringMemoryMiddleware to the public API.
• Deprecate above middleware from old location.
• Deprecate methods from modules that were always meant to be used from the public API:
  • accumulate
  • increment
  • set_custom_attribute
  • set_custom_attributes_for_course_key
• Add additional custom attributes for deprecated classes and methods to make them safer to retire.

Note: Some additional details in the CHANGELOG.rst change in the PR.

JIRA:

ARCHBOM-1584

Testing instructions:

• [X] I will test with an edx-platform sandbox once edx-platform PR is ready.

Merge checklist:

• [x] Merge https://github.com/edx/edx-platform/pull/25504
• [X] All reviewers approved
• [x] CI build is green
• [X] Version bumped
• [X] Changelog record added
• [X] Documentation updated (not only docstrings)
• [x] 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)

[robrap]

Thanks for your thoughts, @idegtiarov. I'll look into whatever is reasonably quick.

1. Black is hopefully coming in the future to help with code consistency.
2. I was trying to squeeze in a step in the right direction, but there will always be more that can be done, especially for existing code that is being moved around.

[idegtiarov]

@robrap Thanks for the answers and clarifications.

[robrap]

@feanil: FYI: I plan on merging, but I wanted to let you know I added these tests for an existing middleware to increase coverage: https://github.com/edx/edx-django-utils/blob/241bb42ae5f511c25ab095018d05966cd509c63d/edx_django_utils/monitoring/tests/test_middleware.py