Enable Real-Time feature roll-out for other teams

If gitlab-com/www-gitlab-com!81580 (merged) is merged, devopsplan become responsible for real-time until the SEG can take it over fully.

We should make it as easy as possible for new real-time features to be created.

• Produce developer documentation so that features that can reuse an existing connection can be created on a self-service basis !62669 (diffs)
• Add developer documentation for introducing new connections, including:
  • Percentage feature flag rollout bands
  • An issue in the devopsplan tracker (perhaps along with Issue template, or reusing feature flag template).
  • (!63235 (merged))
• Publish docs (Slack, Week in review, etc).