Closes#17791
This PR adds ability to cancel workspace builds that are in "pending"
status.
Breaking changes:
- CancelWorkspaceBuild method in codersdk now accepts an optional
request parameter
API:
- Added `expect_status` query parameter to the cancel workspace build
endpoint
- This parameter ensures the job hasn't changed state before canceling
- API returns `412 Precondition Failed` if the job is not in the
expected status
- Valid values: `running` or `pending`
- Wrapped the entire cancel method in a database transaction
UI:
- Added confirmation dialog to the `Cancel` button, since it's a
destructive operation


- Enabled cancel action for pending workspaces (`expect_status=pending`
is sent if workspace is in pending status)

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Co-authored-by: Dean Sheather <dean@deansheather.com>