Add a @grafana/runtime package with backendSrv interface (#16533)

grafana-runtime/tsconfig.json imports query to avoid a build error  ¯\_(ツ)_/¯

public/app/features/teams/state/actions.ts

@@ -1,5 +1,5 @@
 import { ThunkAction } from 'redux-thunk';
-import { getBackendSrv } from 'app/core/services/backend_srv';
+import { getBackendSrv } from '@grafana/runtime';
 import { StoreState, Team, TeamGroup, TeamMember } from 'app/types';
 import { updateNavIndex, UpdateNavIndexAction } from 'app/core/actions';
 import { buildNavModel } from './navModel';