* (WIP) Alerting: Use the forked Alertmanager for remote secondary mode
* fall back to using internal AM in case of error
* remove TODOs, clean up .ini file, add orgId as part of remote AM config struct
* log warnings and errors, fall back to remoteSecondary, fall back to internal AM only
* extract logic to decide remote Alertmanager mode to a separate function, switch on mode
* tests
* make linter happy
* remove func to decide remote Alertmanager mode
* refactor factory function and options
* add default case to switch statement
* remove ineffectual assignment