[amoro-3994] Support Exposing AMS High Availability (HA) Status

[davedwwang]

Why are the changes needed?

I hope to obtain the master-slave status of AMS through HTTP and metrics.

Close #3994.

Brief change log

Introducing a member variable to identify the master/slave status of the AMS. The HealthCheckController and AmsServiceMetrics use this field to retrieve the AMS's master/slave status.