feat(nested folders): add CountDashboardsInFolder (#57847)

* feat(nested folders): add CountDashboardsInFolder

This commit adds a new method to the Dashboard service and stores: CountDashboardsInFolder. The command struct takes a folderUID, but the store implementation still depends on the parent folder ID. This is temporary; eventually we will replace all references to FolderIDs (associated with Dashboards) with folder UIDs.

There are some unfortunate additional test changes that were necessary after generating the service & store mocks; it looks like that hasn't been generated since the last change(s).

* more test updates
* don't forget the service test
* that didn't end up used, so bye for now
* agree to disagree with the linter

pkg/services/dashboards/models.go

@@ -29,3 +29,16 @@ type DashboardSearchProjection struct {
 	FolderTitle string
 	SortMeta    int64
 }
+
+type CountDashboardsInFolderQuery struct {
+	FolderUID string
+}
+
+// Note for reviewers: I wasn't sure what to name this. It's not actually a DTO
+// CountDashboardsInFolderRequest is the request passed from the service to the
+// store layer. The FolderID will be replaced with FolderUID when dashboards are
+// updated with parent folder UIDs.
+type CountDashboardsInFolderRequest struct {
+	FolderID int64
+	OrgID    int64
+}