backend/services: Move GetDashboard from sqlstore to dashboard service (#48971)

* rename folder to match package name
* backend/sqlstore: move GetDashboard into DashboardService

This is a stepping-stone commit which copies the GetDashboard function - which lets us remove the sqlstore from the interfaces in dashboards - without changing any other callers.
* checkpoint: moving GetDashboard calls into dashboard service
* finish refactoring api tests for dashboardService.GetDashboard

pkg/api/team_test.go

@@ -369,10 +369,6 @@ func TestTeamAPIEndpoint_GetTeamPreferences_RBAC(t *testing.T) {
 	_, err := sc.db.CreateTeam("team1", "", 1)
 
 	sqlstore := mockstore.NewSQLStoreMock()
-	sqlstore.ExpectedDashboard = &models.Dashboard{
-		Uid: "home",
-		Id:  1,
-	}
 	sc.hs.SQLStore = sqlstore
 
 	prefService := preftest.NewPreferenceServiceFake()