BackendSrv: Cancellable requests & Observable all the way (#25746)

* 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

* 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

* Fixing tests

* Minor weak

* Improved logic for the showErrorAlert and showSuccessAlert boolean flags, now they work more logically

* Fix issue

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

@@ -171,12 +171,11 @@ export class DataSourceWithBackend<
    */
   async callHealthCheck(): Promise<HealthCheckResult> {
     return getBackendSrv()
-      .get(`/api/datasources/${this.id}/health`)
+      .request({ method: 'GET', url: `/api/datasources/${this.id}/health`, showErrorAlert: false })
       .then(v => {
         return v as HealthCheckResult;
       })
       .catch(err => {
-        err.isHandled = true; // Avoid extra popup warning
         return err.data as HealthCheckResult;
       });
   }