* Alerting: Send configuration and state to the remote Alertmanager on shutdown
* Alerting: Add a sync interval for ApplyConfig in remote secondary mode
* add routine to sync states and configs
* pass a cancellable context to syncRoutine(), remove tests for ApplyConfig, cache last config in memory
* extract logic to update config and state in the remote Alertmanager
* get latest config from the database
* avoid using separate goroutine for updating state and config
* clean up PR
* refactor, comments, tests
* update tests
* remove canceled context from calls to StopAndWait()
* create context with timeout and send config and state to remote Alertmanager
* update tests
* address code review comments
Santiago
23b4568597