Make Plan responsible for real-time rollout

Why is this change being made?

Designates a directly responsible group for the rollout of real-time features on GitLab.

Why devopsplan:

• Maintains momentum on real-time development, gradually shrinking the problem’s surface area until the new SEG is ready to fully take it over.
• Allows the new SEG to focus on the tricky problem of conflict resolution for collaborative editing using CRDTs/OT.
• Plan already have the single WebSocket connection on the issue page that can be reused to implement other real-time features on that page with no additional cost.
• Plan is best-placed to help other teams roll out new features:
  • With general development using GraphQL Subscriptions over WebSockets.
  • By estimating the number of new connections required for each new feature and rolling them out safely at scale.

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the "Maintained by" section in on the page being edited.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files. (this requirement has been removed pending identification of a new DRI for the handbook)