The basic code change is quite simple: #7523

There are two problems left:

testing: make sure the updates we're sending are the ones we expect (e.g., same as before)
fix the "start workspace" case:
- currently we're broadcasting "artificial" events from the server globally for the preparing phase (this includes initial creation/context parsing/resolution as well as image building!)
- with removing the "global" option, other regions would not receive updates for workspace starts in a different region until the pending phase (when ws-manager is called and the first pod is created). This is especially important for image builds - because it extends the "time without update" to multiple minutes potentially - , and more so for prebuilds with image builds - which for 50% of our users always happen in a different (US) cluster
- the ideal solution would be to move image-builder into workspace cluster. But this is non-trivial, has complex dependencies in itself and will not happen soon, so we cannot depend on it
- alternatively, we can try to emulate the updates for the workspace phase preparing by:
  - having something (in either server or bridge) poll the DB for workspace instances in phase preparing, which are not governed by the current bridge
  - if there is a state change: generate an update and distribute it locally

Remove messagebus shovel #7468

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