Insights: contributor tooltip & LocaleHealthSnapshot model changes

[functionzz]

This PR adds a contributor tooltip, displaying corresponding managers/translators/contributors upon hovering over a locales user metric.

Also changes the currently displayed month on the dashboard to represent live statistics rather than potentially stale CHS metrics while maintaining LocaleHealthSnapshot historicity for graphs + MoM comparison. This results are cached daily.

Fixes #4312.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 55.31915% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.50%. Comparing base (d493f14) to head (fb77244).

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[functionzz]

Closing as it is too out of date - working on porting LocaleHealthSnapshots & current dashboard/insights to use ManyToMany User <-> LocaleHealthSnapshots relationships.