Add ability to cancel on-demand scans

This adds the ability to cancel running and pending on-demand scans.

Changelog: added
EE: true

ee/app/assets/javascripts/on_demand_scans/graphql/on_demand_scans.query.graphql

@@ -25,6 +25,7 @@ query onDemandScans(
         id
         path
         createdAt
+        status
         detailedStatus {
           id
           detailsPath