Update CODEOWNERS: rename team-fm-next to team-fm-foundations

[kparkinson-ld]

Summary

Renames the CODEOWNERS team reference from @launchdarkly/team-fm-next to @launchdarkly/team-fm-foundations to reflect the team's new name. This is part of a bulk update across multiple repos in the org.

Review & Testing Checklist for Human

• Verify that @launchdarkly/team-fm-foundations exists as a valid GitHub team in the org (if it doesn't, CODEOWNERS enforcement will break)

Notes

This same change is being applied across all repos that reference @launchdarkly/team-fm-next in their CODEOWNERS files.

Link to Devin session: https://app.devin.ai/sessions/8abe80d07e414755864c1b9c67215686
Requested by: @kparkinson-ld

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