RSocket Protocol v2

[whyoleg]

RSocket protocol v2 has small changes which are incompatible with v1:

• changes resumability spec to make it compatible with QUIC rsocket#312
• provides lease extension spec rsocket#311

Investigate what is needed to support those and how to support both v1 and v2:

• Expose protocol version
• Support selection of V1/V2 on client during connect
• Support conditional select of V1/V2 on server based on setup frame (?) or during accept

Related issues with old API design for those features:

• Lease support #86
• Resume support #87