* 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
This commit adds contact point testing to ngalerts via a new API
endpoint. This endpoint accepts JSON containing a list of
receiver configurations which are validated and then tested
with a notification for a test alert. The endpoint returns JSON
for each receiver with a status and error message. It accepts
a configurable timeout via the Request-Timeout header (in seconds)
up to a maximum of 30 seconds.