SSBC-EM2.2: User can create and track batch changes from the UI

Created by: mrnugget

• ⚠MOST IMPORTANT⚠ Build execution page for per-workspace execution (based on Figma design here)
  • UI: build workflow to create, preview, and then run a batch spec with the new API @eseliger
  • backend: build missing resolver methods on BatchSpecResolver
  • backend: build CancelBatchSpec mutation
  • 2-pane layout: workspaces on the left, details on right
    • workspaces list, see EM3 design
    • details view, see EM3 design
  • go to preview once execution finished
  • cancel button
  • don't upload changeset specs for imported changesets from src CLI in exec mode https://github.com/sourcegraph/src-cli/pull/640
• Improve UX of workspace resolution in UI https://github.com/sourcegraph/sourcegraph/pull/26008
  • Persist and show list of ignored workspaces
  • Persist and show list of unsupported workspaces
  • Persist and show list of workspaces with 0 steps (so that users can see workspaces without having typed in steps in their YAML)
  • Build missing resolver methods that make use of "ignored", "unsupported", etc.