Add Flagsmith as feature flag provider

[emyller]

DESCRIBE YOUR PR

This adds Flagsmith as an option to integrate with feature flags in Sentry.

We made some decisions on how to approach the integrations for now:

• For Change Tracking, we're going with the Generic webhook. It looks like it complies with all existing features in the Sentry UI. We have recently merged the integration with Change Tracking on our end. 🙂
• For Evaluation Tracking, we chose to rely on the OpenFeature SDK with Flagsmith providers. It aligns with our intention to support standardization. We might want to integrate with the Flagsmith SDKs in the future, perhaps within the Sentry feature flags beta period.

Please let us know if that works. I hope the patch looks good!

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• Urgent deadline (GA date, etc.):
• Other deadline:
• None: Not urgent, can wait up to 1 week+

SLA

• Teamwork makes the dream work, so please add a reviewer to your PRs.
• Please give the docs team up to 1 week to review your PR unless you've added an urgent due date to it.
  Thanks in advance for your help!

PRE-MERGE CHECKLIST

Make sure you've checked the following before merging your changes:

• Checked Vercel preview for correctness, including links
• PR was reviewed and approved by any necessary SMEs (subject matter experts)
• PR was reviewed and approved by a member of the Sentry docs team

LEGAL BOILERPLATE

Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. and is gonna need some rights from me in order to utilize my contributions in this here PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.

EXTRA RESOURCES

• Sentry Docs contributor guide

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Name	Status	Preview	Comments	Updated (UTC)
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[bruno-garcia]

Oh this is great! Thanks @emyller

Tagging some folks for review here, approved the vercel preview so we can peek at the rendered site