SSBC-EM3.1: EM3 Designs are implemented for all current features

Created by: eseliger

Outcome: We implemented/aligned the frontend UI with what we have in the designs for EM3. We exclude features that have not been implemented yet, this will be part of the second cut.

• add experimental features
• Do we need to handle the "private" batch spec permission model yet? @mrnugget 0.5d
  • Q: Who's allowed to see shallow batch changes?
    • A: Creator of shallow batch change or site-admin
  • Q: Who can see the list of executions on a Batch Change?
    • A: Creator of batch spec or site-admin
• #27543 (closed) @mrnugget 2d
• #28409 (closed) @mrnugget 1d
• https://github.com/sourcegraph/sourcegraph/issues/28080 @eseliger 2d
• List of executions on a Batch Change (pending permissions) 3d
  • Backend @mrnugget 2d
  • Frontend @eseliger 1d
• Implement the layout from the design for the executions view. @eseliger 5d
  • the apply/preview button on top, so that users discover the preview button
  • left-side pannel with workspace list, that makes it easy to scroll a large number of changesets
  • Hover tooltips on workspaces status, that let the user know what each icon means.
• Implement RetryBatchSpecExecution resolver @mrnugget 2d
  • Add retry batch spec to UI
  • Maybe: Add flag to retry all, even completed