Epic: Simplified Multi-Meta

[geropl]

Summary:
This is the epic for implementing "Simplified Multi-Meta" as specified in this RFC.

Context:

• basically summed up in the RFC

Value:

• enables more Gitpod clusters (e.g., asia) without adding yet another DB
• enables delivering multi-cluster Gitpod to Self-Hosted customers (because it reduces setup complexity)

Measurement:

• messagebus has not cross-cluster dependency anymore
• we got rid of db-sync
• we replaced rabbitmq with a simpler pub/sub implementation (redis pub/sub)

Tasks:

• Remove cross-cluster messagebus dependency
  • Remove PrebuildStatusMaintainer (last non-local writer to messagebus besides ws-manager-bridge) #7436
  • make imagebuild logs independent of cluster locality Stream imagebuild logs directly from pods #7899
  • [messagebus, bridge] Remove messagebus cross-cluster dependency #7523
• get rid of the multi-DB setup
  • Identify meta-instances by name rather DB locality #8271
  • Introduce time measurements for key operations (all/selected API calls)
  • Resolve cross-DB inconsistencies (AT) [db-sync] Add check for cross-DB inconsistencies #7796
  • (optional, if that improves things) Use a read-through cache to improve
  • clean up unsynced DB tables
  • clean up delete jobs (saas vs. self-hosted)
• Replace rabbitmq with Redis pub/sub
  • Replace rabbitmq with Redis pub/sub

[geropl]

Messagebus is done ✔️

Closing this issue in favor of two follow-up epics:

• Epic: Get rid of db-sync #9198
• Epic: Migrate to Installer #9097