Allow FeatureService to switch features per form

[jamie-o-wilkinson]

What problem does this pull request solve?

This commit allows features to be toggled on a per form basis in addition to the global feature flag. This is done in a similar way as per org switching in forms-admin. You can override the default value of a feature flag by providing key value pairs under a forms object, where the key is the form ID. For example:

features:
  flag_test:
    enabled: false
    forms:
      "123": true

We'd like to use this to do some user research for additional submission types with specific forms.

Trello card: https://trello.com/c/5xPfvcTJ

Things to consider when reviewing

• Ensure that you consider the wider context.
• Does it work when run on your machine?
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• Do the commit messages explain why the changes were made?
• Are there all the unit tests needed?
• Has all relevant documentation been updated?

[stephencdaly]

Changes look good. I wonder slightly whether it might be better to use the form ID rather than the slug. The reason for this is that if a form is renamed, the slug changes. I would have thought that if a form is renamed, we wouldn't want features to be disabled. Thoughts?

[DavidBiddle]

I'm inclined to agree with Stephen on using ID instead of slug - as well as being changeable I don't think we enforce uniqueness on form slugs, so ID would target the form we want more specifically

[jamie-o-wilkinson]

Good points, thanks both! I've updated to use form ID instead of slug. This makes the settings file less readable, but we can just go to admin to find out which form maps to which ID for now if need be.

[stephencdaly]

Changes look good and I've tested it locally by modifying an existing feature flag to use this.
Just one minor comment.

[DavidBiddle]

Works for me locally, code looks good, nice readable tests 🎉

[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud