project onboarding: Feature Flag Semantic Conventions

[svrnm]

The Feature Flag Semantic Conventions SIG project proposal has been approved, here are the todos to get them started:

• [ ] Project Board
• [ ] Add Meeting Times, GC Liaison, Slack Channel, Google Doc to sigs.yml
• [ ] SIG Channel
• [ ] GitHub Teams

cc @dyladan @AlexanderWert @beeme1mr

[trask]

@open-telemetry/semconv-feature-flag-approvers created with following maintainers:

• @dyladan
• @AlexanderWert