feat: Backend support for feature health

[khvn26]

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• I have added information to docs/ if required so people know about the feature!
• I have filled in the "Changes" section below?
• I have filled in the "How did you test this code" section below?
• I have used a Conventional Commit title for this Pull Request

Changes

• Auditable feature health events
• Sample feature health event provider
• Feature health event ingestion webhook with signed paths
• "Unhealthy" system tag automatically added to features with corresponding feature health events

To create a Sample feature health provider, perform the following request:

curl -x POST http://<base-api-url>/api/v1/projects/<project-id>/feature-health/providers -H 'authorization: Token <user token>' --data-raw '{"type": "Sample"}'

or use the admin interface.

Request the resulting webhook URL:

curl -x POST http://<base-api-url>/api/v1/feature-health/<webhook-hash> --data-raw '{"environment": "<your-env-name>", "status": "unhealthy", "feature": "<your-feature-name>"}'

Observe the new system tag being added to your feature of choice.

Get a list of latest feature events per feature-provider pair:

curl http://<base-api-url>/api/v1/projects/<project-id>/feature-health/events -H 'authorization: Token <user token>'

How did you test this code?

Please describe.

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3 Skipped Deployments

Name	Status	Preview	Comments	Updated (UTC)
docs	⬜️ Ignored (Inspect)	Visit Preview		Jan 28, 2025 7:54pm
flagsmith-frontend-preview	⬜️ Ignored (Inspect)	Visit Preview		Jan 28, 2025 7:54pm
flagsmith-frontend-staging	⬜️ Ignored (Inspect)	Visit Preview		Jan 28, 2025 7:54pm

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Uffizzi Preview deployment-60083 was deleted.

[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-api-test:pr-5023	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-api:pr-5023	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-frontend:pr-5023	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-5023	Finished ✅	Results ✅

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.43%. Comparing base (ecd409b) to head (1486737).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5023      +/-   ##
==========================================
+ Coverage   97.40%   97.43%   +0.03%     
==========================================
  Files        1193     1214      +21     
  Lines       41763    42224     +461     
==========================================
+ Hits        40678    41140     +462     
+ Misses       1085     1084       -1     

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[matthewelwell]

Approved with a few remaining minor comments.