feat: Add deprecation warning to code owner celery task decorator

[rahulkanneri-2u]

Adds a DeprecationWarning and a monitoring custom attribute to set_code_owner_attribute / set_code_owner_attribute_from_module, to signal the upcoming removal and give visibility into which callers still use it before it is removed.

Refs #469

Description:

Adds a DeprecationWarning and a deprecated_code_owner_celery_monitoring monitoring custom attribute inside set_code_owner_attribute / set_code_owner_attribute_from_module. This is purely additive (no behavior change) and gives downstream teams a signal, plus dashboard visibility into which modules still call the decorator, ahead of its eventual removal.

JIRA:

#469

Dependencies:

None.

Merge deadline:

None currently. The Willow branch cut was delayed to early January 2027, so there's no immediate deadline pressure on this change.

Installation instructions:

None.

Testing instructions:

1. Decorate a function with @set_code_owner_attribute (or call set_code_owner_attribute_from_module directly).
2. Call the decorated function.
3. Expect a DeprecationWarning to be raised, and a deprecated_code_owner_celery_monitoring custom attribute to be set with the calling module name.
4. If no warning is raised, or the custom attribute is missing - check failed. See test_set_code_owner_attribute_deprecation_warning, test_set_code_owner_attribute_from_module_deprecation_warning, and test_set_code_owner_attribute_from_module_deprecated_custom_attribute in test_utils.py.

Reviewers:

• tag reviewer

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:

List any concerns about this PR - inelegant
solutions, hacks, quick-and-dirty implementations, concerns about
migrations, etc.

[vgulati-apphelix]

@rahulkanneri-2u Please update the ticket reference to github ticket id.