Implement k8s count handler (#97955)

* Implement k8s count handler

* Fix endpoint

* Fix type converstions

* Add tests for foldercounts

* Add more tests

* Only use sql-fallback if no values in unistore

* Update gomod

* Fix test

* Update pkg/api/folder_test.go

Co-authored-by: Bruno Abrantes <bruno.abrantes@grafana.com>

* Go.mod

---------

Co-authored-by: Bruno Abrantes <bruno.abrantes@grafana.com>

pkg/tests/apis/folder/folders_test.go

@@ -93,7 +93,7 @@ func TestIntegrationFoldersApp(t *testing.T) {
 				]
 			  },
 			  {
-				"name": "folders/count",
+				"name": "folders/counts",
 				"singularName": "",
 				"namespaced": true,
 				"kind": "DescendantCounts",