Backend changes to for label membership to respect team_id

[lucasmrod]

Related user story

#33760

Task

• Implement server side changes and API changes defined in Team admin, maintainer, and GitOps users can create labels via GitOps (YAML) #33760.
• No API changes here, all backend internal changes like distributed/{read|write}, host transfer, etc. (label membership to respect team_id).
• Ensure team deletes cascade properly to team labels (including label membership cleanup).

[iansltx]

Added a note on deletions because due to lack of fkeys in e.g. label membership we don't get those for free.