Explore: Add Mixed Datasource (#53429)

* Toggle on the mixed mode option

* Ensure switching to mixed gives existing query prev datasource

* WIP - Populate datasource when switching between mixed and not

* WIP - handle change from mixed

* Remove preimport filter, refine filter to work for queries

* WIP debugging datasource transition

* Ensure creating a new query gets target data source if switching with no matches between

* Add mixed datasource to rich history display

* Cleanup console logs, add relevant comments

* Add feature toggle for mixed datasource

* Fix Wrapper tests

* Fix tests!

* Fix test types and add feature tracking

* Remove unnecessary default, remove explore/mixed workarounds for D2E

* Move display text logic to mixed datasource file

* Add in the default query parameters to a generated empty query

* Condense some code

* Apply suggestions from code review

Co-authored-by: Giordano Ricci <me@giordanoricci.com>

* Add more logic around mixed datasource being off for explore

* Build out logic to handle different datasource scenarios

* Add tests

* Finalize last test

* Fix mixed URL with mixed ds off, and relevant test

* Fix datasource to explore workflow

* Add datasource change function, call import queries if needed

* add logic for changing single query ds

Co-authored-by: Giordano Ricci <me@giordanoricci.com>

public/app/features/explore/state/datasource.ts

@@ -2,6 +2,7 @@
 import { AnyAction, createAction } from '@reduxjs/toolkit';
 
 import { DataSourceApi, HistoryItem } from '@grafana/data';
+import { reportInteraction } from '@grafana/runtime';
 import { RefreshPicker } from '@grafana/ui';
 import { stopQueryState } from 'app/core/utils/explore';
 import { ExploreItemState, ThunkResult } from 'app/types';
@@ -44,6 +45,11 @@ export function changeDatasource(
     const { history, instance } = await loadAndInitDatasource(orgId, { uid: datasourceUid });
     const currentDataSourceInstance = getState().explore[exploreId]!.datasourceInstance;
 
+    reportInteraction('explore_change_ds', {
+      from: (currentDataSourceInstance?.meta?.mixed ? 'mixed' : currentDataSourceInstance?.type) || 'unknown',
+      to: instance.meta.mixed ? 'mixed' : instance.type,
+      exploreId,
+    });
     dispatch(
       updateDatasourceInstanceAction({
         exploreId,