Implement ADR on toggle-life-expectancy

[robrap]

This ticket is for implementing ADR 0005-toggle-life-expectancy.rst. Please review for details.

Implementation/rollout details:

• [ ] Introduce toggle_life_expectancy annotation with values of "temporary" or "permanent" as optional.
• [ ] Introduce toggle_permanent_justification as a free-form annotation as optional.
• [ ] Legacy toggle_use_cases annotation should be made optional (until removed).
• [ ] Update how-to document toggles as appropriate.
• [ ] Update existing annotated toggles with these new annotations. See additional notes for details.
• [ ] Make toggle_permanent_justification required for "permanent" toggles.
• [ ] Make toggle_target_removal_date required for the new definition of "temporary" toggles, and no longer for the old definition.
• [ ] Update OEP-17 as appropriate or create separate ticket. See additional notes.

Additional Notes:

• This requires working in the code-annotations config, toggles code and docs, toggle linting, and other repos containing annotated toggles.
  • Could this help be moved to a toggle doc?
• When adding the new annotations, there are a number of adjustments we may want to make at once.
  • We may need to relax linting rules first. When we do this, we may want to move faster on this part.
  • Use of None or 'n/a' should be avoided. For optional annotations, they should just be removed instead.
  • If marking a toggle as "temporary", we should note ensure there is a toggle_target_removal_date. If there is none, we could just add 3 months from the time of this PR, and note in the commit that we have filled these all in.
  • If marking a toggle as "permanent", but we are unsure, see ADR for language for toggle_permanent_justification. Could be something like: Tentatively marking as permanent. A DEPR could be used to confirm.
  • See https://openedx.atlassian.net/wiki/spaces/AC/pages/2554331530/Toggles+and+Settings+Documentation for other clean-up notes.
• The how-to document toggles doc might need multiple updates, unless the initial update pretends like annotation requirements are complete.
  • Additionally, the ADR has other notes about how to help people fill in the new annotations.
• Note that OEP-17 is outdated in other ways from these docs.
• This would resolve a possible bug where required fields for temporary use case might be missed when multiple use cases are listed.

[robrap]

Note: I'm happy to be a guide and reviewer if someone picks this up.

[Yagnesh1998]

assign me

[Yagnesh1998]

@robrap I will assign it myself and start working on it shortly after my one pending DEPR ticket will be completed is that makes sense.