Prometheus: Run exemplars explore queries through backend (#39531)

* Prometheus: Run Explore both queries trough backend

* Refactor, simplify

* Set default values for query type selector

* Run multiple queries as one query trough backend

* Remove trailing newlines

* Pass utcOffset

* Remove trailing comma

* WIP: Implementatioon of exemplars

* add sampling for exemplars

* Refactor to use response as custom metadata

* Simplify processing of exemplars

* Update, clean up

* Refactor the way how we get available exemplars

* Simplify exemplars disabling and running on frontend

* Add tests

* Update toggle

* Remove console log

* Fix go linting

* Fix e2e test

* Trigger Build

* Compare lengts, small fix

* Remove duplicated time check

* Address feedback

* Remove redundant ! as not needed

* Update

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

@@ -3,8 +3,6 @@ import { render, RenderResult } from '@testing-library/react';
 import { PromQueryEditorByApp } from './PromQueryEditorByApp';
 import { CoreApp } from '@grafana/data';
 import { noop } from 'lodash';
-import { Observable } from 'rxjs';
-import { first } from 'rxjs/operators';
 import { PrometheusDatasource } from '../datasource';
 import { testIds as alertingTestIds } from './PromQueryEditorForAlerting';
 import { testIds as regularTestIds } from './PromQueryEditor';
@@ -20,7 +18,6 @@ function setup(app: CoreApp): RenderResult {
       getLabelKeys: () => [],
       metrics: [],
     },
-    exemplarErrors: new Observable().pipe(first()),
   } as unknown) as PrometheusDatasource;
 
   return render(