Update iproto replication docs to 3.0

[p7nov]

Resolves #3503, #3886

• Add new IPROTO_BALLOT key IPROTO_BALLOT_INSTANCE_NAME
• Add new IPROTO_FETCH_SNAPSHOT key IPROTO_SERVER_VERSION
• Add IPROTO_INSTANCE_NAME and IPROTO_REPLICASET_NAME keys

Deployment:

• Replication requests: https://www.tarantool.io/en/doc/latest/reference/internals/iproto/replication/
• iproto keys: https://docs.d.tarantool.io/en/doc/gh-3505-iproto-replication-3x/reference/internals/iproto/keys/#general-replication

[sergepetrenko]

Thanks for the patch!