* 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
* add config struct for remote secondary forked Alertmanager
* use errgroups for sync operations
* use waitgroup instead of errgroup
* remove helper method to sync AMs
* check for errors instead of bool syncErr
* Alerting: Add a sync interval for ApplyConfig in remote secondary mode
* remove out of scope code
* remove parentheses after CleanUp for consistency in test comments
* Add comment to ApplyConfig
* Alerting: Add an empty Forked Alertmanager
* Alerting: Add methods for silences to the forked Alertmanager
* check for errors in tests
* make linter happy
* Alerting: Add methods for alerts to the forked Alertmanager
* Alerting: Add methods for receivers to the forked Alertmanager
* Alerting: Add TestTemplate method to the forked Alertmanager
* make linter happy
* separate into both forked AMs
* fix tests
* Alerting: Add lifecycle methods to the forked Alertmanager
* Alerting: Add an empty Forked Alertmanager
* Alerting: Add methods for silences to the forked Alertmanager
* check for errors in tests
* make linter happy
* Alerting: Add methods for alerts to the forked Alertmanager
* Alerting: Add methods for receivers to the forked Alertmanager
* Alerting: Add TestTemplate method to the forked Alertmanager
* make linter happy
* separate into both forked AMs
* fix tests
* Alerting: Add an empty Forked Alertmanager
* Alerting: Add methods for silences to the forked Alertmanager
* check for errors in tests
* make linter happy
* Alerting: Add methods for alerts to the forked Alertmanager
* Alerting: Add methods for receivers to the forked Alertmanager
* make linter happy
* separate into both forked AMs
* fix tests
* rename testErr -> expErr
* Alerting: Add an empty Forked Alertmanager
* Alerting: Add methods for silences to the forked Alertmanager
* check for errors in tests
* make linter happy
* Alerting: Add methods for alerts to the forked Alertmanager
* make linter happy
* separate into both forked AMs
* rename testErr -> expErr
* Alerting: Add an empty Forked Alertmanager
* Alerting: Add methods for silences to the forked Alertmanager
* check for errors in tests
* make linter happy
* make linter happy
* Alerting: Add methods for silences to the forked Alertmanager
