Enhance client protocol to propagate last seen state IDs for multiple nameservices.

The RPCHeader in the client protocol currently contains a single value to indicate the last seen state ID for a namenode.

optional int64 stateId = 8; // The last seen Global State ID

When there are multiple namenodes, such as in router based federation, the headers need to carry the state IDs for each of these nameservices that are part of the federation.

This change is a prerequisite for HDFS-13522: RBF: Support observer node from Router-Based Federation