* 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>