SSBC: View the position of my batch change in the queue

Created by: malomarrec

User problem

When I submit a new batch change, all executors might be busy for a while running other batch changes. Fair scheduling will be addressed by #26895, but regardless of what scheduling principle is used, as a user I want to know where my batch change is in the queue.

The ideal answer to "when will my batch change run" is, in order of usefulness:

• a timeline (sounds hard, frustrating, not worth it)
• the number of workspaces that need to be processed before mine
• the number of batch changes before mine

Proposal

Needs design.