Grafana: Replace magic number with a constant variable in response status (#80132)

* Chore: Replace response status with const var

* Apply suggestions from code review

Co-authored-by: Sofia Papagiannaki <1632407+papagian@users.noreply.github.com>

* Add net/http import

---------

Co-authored-by: Sofia Papagiannaki <1632407+papagian@users.noreply.github.com>

pkg/services/dashboardimport/api/api.go

@@ -73,7 +73,7 @@ func (api *ImportDashboardAPI) ImportDashboard(c *contextmodel.ReqContext) respo
 	}
 
 	if limitReached {
-		return response.Error(403, "Quota reached", nil)
+		return response.Error(http.StatusForbidden, "Quota reached", nil)
 	}
 
 	req.User = c.SignedInUser