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/language_provider.ts

@@ -9,7 +9,7 @@ import {
   addLimitInfo,
   fixSummariesMetadata,
   parseSelector,
-  processHistogramLabels,
+  processHistogramMetrics,
   processLabels,
   roundSecToMin,
 } from './language_utils';
@@ -123,8 +123,7 @@ export default class PromQlLanguageProvider extends LanguageProvider {
     await this.fetchLabels();
     this.metrics = (await this.fetchLabelValues('__name__')) || [];
     this.metricsMetadata = fixSummariesMetadata(await this.request('/api/v1/metadata', {}));
-    this.processHistogramMetrics(this.metrics);
-
+    this.histogramMetrics = processHistogramMetrics(this.metrics).sort();
     return [];
   };
 
@@ -132,14 +131,6 @@ export default class PromQlLanguageProvider extends LanguageProvider {
     return this.labelKeys;
   }
 
-  processHistogramMetrics = (data: string[]) => {
-    const { values } = processHistogramLabels(data);
-
-    if (values && values['__name__']) {
-      this.histogramMetrics = values['__name__'].slice().sort();
-    }
-  };
-
   provideCompletionItems = async (
     { prefix, text, value, labelKey, wrapperClasses }: TypeaheadInput,
     context: AutocompleteContext = {}