LibraryElements: Creates usage stats for panels and variables (#34476) (#34555)

* LibraryPanels: Adds usage collection

* Refactor: renames Panel and Variable consts

* Chore: initialize stats

* Refactor: moves library element migrations to migration namespace

(cherry picked from commit 7204a64717)

Co-authored-by: Hugo Häggmark <hugo.haggmark@grafana.com>

pkg/services/librarypanels/librarypanels.go

@@ -76,7 +76,7 @@ func (lps *LibraryPanelService) LoadLibraryPanelsForDashboard(c *models.ReqConte
 			continue
 		}
 
-		if libraryelements.LibraryElementKind(elementInDB.Kind) != libraryelements.Panel {
+		if models.LibraryElementKind(elementInDB.Kind) != models.PanelElement {
 			continue
 		}
 

pkg/services/librarypanels/librarypanels_test.go

@@ -493,7 +493,7 @@ func TestConnectLibraryPanelsForDashboard(t *testing.T) {
 			  "description": "Unused description"
 			}
 		`),
-				Kind: int64(libraryelements.Panel),
+				Kind: int64(models.PanelElement),
 			})
 			require.NoError(t, err)
 			dashJSON := map[string]interface{}{
@@ -783,7 +783,7 @@ func scenarioWithLibraryPanel(t *testing.T, desc string, fn func(t *testing.T, s
 			  "description": "A description"
 			}
 		`),
-			Kind: int64(libraryelements.Panel),
+			Kind: int64(models.PanelElement),
 		}
 		resp, err := sc.elementService.CreateElement(sc.reqContext, command)
 		require.NoError(t, err)