Feature Flag Improvements

[Mephistic]

Detailed Description We should upgrade the feature flag system so that we can set the value of flags without requiring a code change and deploy.

Reason for the Suggestion The current feature flag system is useful for merging changes before we're fully ready to make them available in production, but it's limited by the fact that the flags are just static constants. This means that we have to set the value of the flags at merge time, and will need a new merge and deploy in order to actually change a flag value for an environment. This makes it impractical to test the different states of the flag in the dev environment before rolling out to production, which reduces our confidence in our ability to safely deploy to production.

A more robust flag system would have helped catch a bug in a recent deploy. We knew there was a specific flag state we wanted to test on the dev environment, but weren't able to configure the dev environment to set that flag.

Success Criteria

• [ ] Ability to update feature flag values without a deploy

Additional Context

• Statically generated pages are pre-rendered at build-time. We may need to re-validate these pages if a relevant flag value changes.
• It's possible that a light weight implementation could deliver most of the needed value here (e.g. if we just allow overrides to flags from a cookie/localStorage/query param - that should suffice for testing most front end work, though it wouldn't suffice for actual feature rollouts and could have unintuitive, sharp edges around next.js caching/static generation).
• There are third party solutions that provide feature flag support - things like PostHog, Unleash, Flagsmith, etc. They're likely overkill for our needs but worth mentioning.

Checklist

• [x] I have checked if this enhancement is not already suggested
• [x] I have explained the enhancement in detail

[Mephistic]

Looks like the query param route may be the way to go here - it's intuitive for both devs and non-devs to use, and has the advantage of making it easy to pass links to the site with different flag states.

Statically generated pages would be nice to have for the MVP here, but we don't have many of those and likely won't need feature flagging on the ones we do have (e.g. the Learn Testimony pages), so I don't think it's worth going out of our way to include those in this issue.

The third-party solutions are definitely overkill for our immediate needs (and our foreseeable future needs).

[Mephistic]

The query param pass on this is implemented. There are certainly potential future improvements around flagging, but we can open a new issue for those as we hit pain points with the current method.