API: return resource ID when deleting datasource with UID and library element (#41342)

* API: return resource ID when deleting datasource and library element

* keep status codes consistent

* fix element ID

* add test

* improve response struct

* update endpoints documentation

* LibraryElementIDResponse -> DeleteLibraryElementResponse

pkg/services/libraryelements/libraryelements_delete_test.go

@@ -1,6 +1,7 @@
 package libraryelements
 
 import (
+	"encoding/json"
 	"testing"
 
 	"github.com/grafana/grafana/pkg/components/simplejson"
@@ -17,11 +18,17 @@ func TestDeleteLibraryElement(t *testing.T) {
 			require.Equal(t, 404, resp.Status())
 		})
 
-	scenarioWithPanel(t, "When an admin tries to delete a library panel that exists, it should succeed",
+	scenarioWithPanel(t, "When an admin tries to delete a library panel that exists, it should succeed and return correct ID",
 		func(t *testing.T, sc scenarioContext) {
 			sc.ctx.Req = web.SetURLParams(sc.ctx.Req, map[string]string{":uid": sc.initialResult.Result.UID})
 			resp := sc.service.deleteHandler(sc.reqContext)
 			require.Equal(t, 200, resp.Status())
+
+			var result DeleteLibraryElementResponse
+			err := json.Unmarshal(resp.Body(), &result)
+
+			require.NoError(t, err)
+			require.Equal(t, sc.initialResult.Result.ID, result.ID)
 		})
 
 	scenarioWithPanel(t, "When an admin tries to delete a library panel in another org, it should fail",