Feature request: hot standby and failover

[edeykholt]

As a Signify client of KERIA, I want high availability even in the case of a failure of my current KERIA instance or its infrastructure.

Success Criteria: A KERIA instance maintains a hot standby structure to a hot standby KERIA instance. When a KERIA goes down, the failover KERIA becomes primary. A Signify client will suffer minimal or no downtime of its functionality during a failover.

This is related to disaster recover (#37).

[2byrds]

Adding for consideration to top 10 #240