Feature/mrtable

[jinzha]

MR table support:

• SignatureProvider: sign request content for those requests need to get obo token or with obo token

• Added 3 new requests: AddReplicaRequest: add replica on a table DropReplicaRequest: drop replica on a table GetReplicaStatsRequest: get replication stats information

• TableResult: added new fields SchemaState schemaState boolean isLocalReplicaInitialized Replica[] replicas

• Added TableNotReadyException The exception is thrown when the multi-region table is not ready for DML operations before the initialization completed.

[gmfeinberg]

A CHANGELOG entry for the user-visible additions needs to be added