This resolution heavily revises [1] based on
feedback from the July 11, 2023 TC meeting.
1. EM is rename to Unmaintained.
2. Branch deletion and creation under unmaintained/.
3. New Gerrit group responsible for the branch.
4. Mention of TC maintaining a checklist and process.
[1]. https://review.opendev.org/c/openstack/governance/+/887966
Change-Id: I72ac1eab3c6b1b55b4f2bc017d5befaaee138f5f