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

public/app/features/admin/state/actions.ts

@@ -38,11 +38,12 @@ export function loadAdminUserPage(userId: number): ThunkResult<void> {
       dispatch(userAdminPageLoadedAction(true));
     } catch (error) {
       console.log(error);
-      error.isHandled = true;
+
       const userError = {
         title: error.data.message,
         body: error.data.error,
       };
+
       dispatch(userAdminPageFailedAction(userError));
     }
   };