feat(flags): Add featureFlagsIntegration for custom tracking of flag evaluations

[aliu39]

Follow-up to #14207.

Sentry integration for buffering feature flags manually with an API and automatically capturing them on error events.

[lforst]

blocking because I don't want this to get accidentally merged nvm

unblock

[aliu39]

@lforst I discussed with @billyvg and we're ok with making setFlag a top-level API fx (gonna rename it captureFlag). It'll log an error and return if the integration isn't installed. Does this sound good? Lmk and I can make the changes tomorrow

[lforst]

@lforst I discussed with @billyvg and we're ok with making setFlag a top-level API fx (gonna rename it captureFlag). It'll log an error and return if the integration isn't installed. Does this sound good? Lmk and I can make the changes tomorrow

@aliu39 Sounds great. I would personally call it setFlag or addFlag, since "capture" sounds to me like sending a 1-time thing to Sentry but that's up to you.

[billyvg]

addFlag sounds good to me, setFlag is a bit confusing because it sounds like you're setting/changing the flag value.

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
621	1	620	300

View the top 1 failed tests by shortest run time

client-app-routing-instrumentation.test.ts Creates a navigation transaction for app router routes

Stack Traces | 30s run time

client-app-routing-instrumentation.test.ts:19:5 Creates a navigation transaction for app router routes

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