AO3-7135 Record canonized/decanonized dates on tags

[pmonfort]

Pull Request Checklist

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• Have you added tests for any changed functionality?
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Issue

https://otwarchive.atlassian.net/browse/AO3-7135

Purpose

Adds two new datetime columns (canonized_at and decanonized_at) to the tags table to record when a tag was most recently canonized or decanonized.

• A before_save callback sets canonized_at when a tag becomes canonical, and decanonized_at when it becomes non-canonical.
• The tag edit page displays "Last canonized on [datetime] UTC" and "Last decanonized on [datetime] UTC" to admins (superadmin, policy_and_abuse, tag_wrangling), directly below the "last edited" information. Sentences are omitted when the corresponding date is nil.
• Both fields are indexed in Elasticsearch and exposed as sort options ("Date Canonized", "Date Decanonized") in tag search.

Testing Instructions

1. Log in as a tag wrangler.
2. Create a new tag (non-canonical). Edit it, you should not see "Last canonized on" or "Last decanonized on".
3. Create a new canonical tag. Edit it, you should not see the dates (wranglers don't see them).
4. Log out.
5. Log in as an admin with superadmin, policy_and_abuse, or tag_wrangling role.
6. Edit the non-canonical tag from step 2, you should not see any canonization dates.
7. Check "Canonical", save, and re-edit, you should see "Last canonized on [datetime] UTC"
8. Uncheck "Canonical", save, and re-edit, you should see both "Last canonized on" and "Las
9. Edit the canonical tag from step 3, you should see "Last canonized on [datetime] UTC" on
10. Find a tag that was canonized before this deployment and decanonize it, it should shotetime] UTC" only (no canonized date since that happened before the migration).
11. Log out.
12. Search > Tags, verify "Date Canonized" and "Date Decanonized" appear in the "Sort by" d
13. Sort by "Date Canonized" descending, recently canonized tags should appear first.
14. Sort by "Date Decanonized" descending, recently decanonized tags should appear first.

Credit

Pablo Monfort (he/him)

[sarken]

Looking pretty good! Could you add a test in features/tags_and_wrangling/tag_search.feature to check the results of sorting?

[sarken]

Once you save changes, you should be redirected to the tag edit page, so this step would ideally be unnecessary... Did you try it without? (I can understand if you did and it failed due to the test running too quickly, but I wanted to ask just the same.)

[sarken]

Do we need strftime here? I get the desired format just by using utc (although, to be fair, I tried it on @tag.updated_at since that was what I had handy)