chore(codeowners): add FF&E ownership for flags and openfeature packages

[ncreated]

What does this PR do?

Adds @DataDog/feature-flagging-and-experimentation-sdk as a code owner of packages/core/src/flags/ and packages/react-native-openfeature/, alongside @DataDog/rum-mobile and @DataDog/rum-mobile-reactnative.

Motivation

FF&E is actively developing in these paths (#1326, #1330, #1331, #1332) but has no code-review ownership configured today, so they can't review their own changes. Co-ownership (rather than exclusive) keeps RUM able to unblock a merge if FF&E reviewers are unavailable — a single approval from any listed team is enough.

Additional Notes

Once this merges to develop, it won't automatically apply to the already-open FFL-2666 stack (#1326 → #1330 → #1331 → #1332) — each of those branches needs to pick up this change via rebase/merge before code-owner review kicks in on their PRs.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)
• If this PR is auto-generated, please make sure also to manually update the code related to the change

[Copilot]

Pull request overview

Adds Feature Flags & Experimentation (FF&E) team as additional codeowners for the feature-flag core implementation and the React Native OpenFeature package, ensuring FF&E can review changes in the areas they actively develop while preserving existing RUM ownership.

Changes:

• Adds @DataDog/feature-flagging-and-experimentation-sdk as a codeowner for /packages/core/src/flags/.
• Adds @DataDog/feature-flagging-and-experimentation-sdk as a codeowner for /packages/react-native-openfeature/.
• Adds a more specific CODEOWNERS entry for /packages/react-native-openfeature/README.md to include FF&E (and maintain docs ownership).

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.