CARL should track the state of a peer

[kKdH]

Currently CARL does not track the state of a peer (EDGAR). To be more precise CARL does not "know" whether a peer:

• is available to be used in a cluster.
• is blocked because it is already part of a cluster.
• ~~is in a failure state and therefore cant be used in a cluster.~~

It is currently possible to deploy a cluster even if the related peers are offline. This behavior is intended. But the problem is, that is in-transparent to a user or external program that the cluster/peer is in an invalid (unhealthy) state.

We have already elaborated a set of states for a peer here

• [x] CARL tracks the state of all connected peers
• [x] Implement gRPC Interface to provide status of peer