DataSourceWithBackend: Switch to new Observable fetch api (#26043)

* BackendSrv: Observable all the way POC

* starting to unify code paths

* tests pass

* Unified error handling

* Single request path and error handling

* Fixed ts issue

* another ts issu

* Added back old requestId cancellation

* Slow progress trying to grasp the full picture of cancellation

* Updates

* refactoring

* Remove a bunch of stuff from backendSrv

* Removed another function

* Do not show error alerts for data queries

* Muu

* Updated comment

* DataSourceWithBackend: Switch to new Observable fetch api

* fixed ts issue

* unify request options type

* Made query inspector subscribe to backendSrv stream instead of legacy app events

* Add back support for err.isHandled to limit scope

* never show success alerts

* Updated tests

* use ovservable in test

* remove processResponse

* remove processResponse

* trying to get tests to pass :(

* no need for the extra tests

* Fixed processsing

* Fixed tests

* Updated tests to mock fetch call

* lint fixes

Co-authored-by: Ryan McKinley <ryantxu@gmail.com>

packages/grafana-runtime/src/utils/DataSourceWithBackend.ts

@@ -7,7 +7,8 @@ import {
   DataSourceJsonData,
   ScopedVars,
 } from '@grafana/data';
-import { Observable, from, of } from 'rxjs';
+import { Observable, of } from 'rxjs';
+import { map, catchError } from 'rxjs/operators';
 import { config } from '..';
 import { getBackendSrv } from '../services';
 import { toDataQueryResponse } from './queryResponse';
@@ -101,42 +102,23 @@ export class DataSourceWithBackend<
       body.to = range.to.valueOf().toString();
     }
 
-    const req: Promise<DataQueryResponse> = getBackendSrv()
-      .datasourceRequest({
+    return getBackendSrv()
+      .fetch({
         url: '/api/ds/query',
         method: 'POST',
         data: body,
         requestId,
       })
-      .then((rsp: any) => {
-        const dqs = toDataQueryResponse(rsp);
-        if (this.processResponse) {
-          return this.processResponse(dqs);
-        }
-        return dqs;
-      })
-      .catch(err => {
-        err.isHandled = true; // Avoid extra popup warning
-        const dqs = toDataQueryResponse(err);
-        if (this.processResponse) {
-          return this.processResponse(dqs);
-        }
-        return dqs;
-      });
-
-    return from(req);
+      .pipe(
+        map((rsp: any) => {
+          return toDataQueryResponse(rsp);
+        }),
+        catchError(err => {
+          return of(toDataQueryResponse(err));
+        })
+      );
   }
 
-  /**
-   * Optionally augment the response before returning the results to the
-   *
-   * NOTE: this was added in 7.1 for azure, and will be removed in 7.2
-   * when the entire response pipeline is Observable
-   *
-   * @internal
-   */
-  processResponse?(res: DataQueryResponse): Promise<DataQueryResponse>;
-
   /**
    * Override to skip executing a query
    *