* Create API test for overwriting invalid alertmanager config
* Avoid requiring alertmanager readiness for config changes
* AlertmanagerSrv depends on functionality rather than concrete types
* Add test for non-ready alertmanagers
* Additional cleanup and polish
* Back out previous integration test changes
* Refactor of tests incorrectly caused a test to become redundant
* Use pre-existing fake secret service
* Drop unused interface
* Test against concrete MultiOrgAlertmanager re-using fake infra from other tests
* Fix linter error
* Empty commit to rerun checks
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