Prometheus: Add info that using Loki as Prometheus data source is no longer supported and might stop working (#34650)

* Add information that Loki as Prometheus data source is not supported

* Fix ugly error when loki as prometheus used

* Refactor, add test

* Fix type error

* Fix test by passing missing method

* Update public/app/plugins/datasource/prometheus/query_hints.ts

* Remove optionality in prop

public/app/plugins/datasource/prometheus/components/PromQueryEditorByApp.test.tsx

@@ -12,6 +12,7 @@ import { testIds as regularTestIds } from './PromQueryEditor';
 function setup(app: CoreApp): RenderResult {
   const dataSource = ({
     createQuery: jest.fn((q) => q),
+    getInitHints: () => [],
     getPrometheusTime: jest.fn((date, roundup) => 123),
     languageProvider: {
       start: () => Promise.resolve([]),