feat(service): unify database and storage backups on one page

List service database schedules with volume backups, add a database
picker when creating scheduled DB backups from the service page, and
cover the unified table and create flow in tests.

resources/css/app.css

@@ -2238,6 +2238,11 @@ input[type="search"]::-webkit-search-results-decoration {
     min-width: 50rem;
 }
 
+.service-backup-table-grid {
+    grid-template-columns: minmax(10rem, 1.7fr) 6rem minmax(7rem, 0.8fr) 7.5rem 6.5rem minmax(8rem, 1fr);
+    min-width: 45rem;
+}
+
 /* Persistent storage volumes: Name | Source | Destination | [PR suffix] | Backup | [Actions] */
 .volumes-table-grid-readonly {
     grid-template-columns: minmax(12rem, 1.5fr) minmax(8rem, 1fr) minmax(8rem, 1fr) 5rem;