Add v2 channel service definition

[damiannolan]

Summary

The feat/ibc-eureka branch contains a service defintion called PacketMsg which is generated to a packet-server directory which houses the ibc protocol v2 code flow.

Inline with rebranding and refactoring the packet-server to v2 channel, we should redefine this service definition as the new v2 channel MsgServer service.

Proposal

The proposed service defintion is as follows:

service Msg {
  option (cosmos.msg.v1.service) = true;

  // SendPacket defines a rpc handler method for MsgSendPacket.
  rpc SendPacket(MsgSendPacket) returns (MsgSendPacketResponse);

  // RecvPacket defines a rpc handler method for MsgRecvPacket.
  rpc RecvPacket(MsgRecvPacket) returns (MsgRecvPacketResponse);

  // Timeout defines a rpc handler method for MsgTimeout.
  rpc Timeout(MsgTimeout) returns (MsgTimeoutResponse);

  // Acknowledgement defines a rpc handler method for MsgAcknowledgement.
  rpc Acknowledgement(MsgAcknowledgement) returns (MsgAcknowledgementResponse);
}

This reduces the channel v2 service to 4 explicit rpc handler funcs, previous handshake code included in v2 in no longer necessary following the ibc eureka/v2 design.

Breakdown

This issue can be broken down into the following tasks and included in well-scoped pull requests:

• Add SendPacket rpc skeleton and associated msg types #7349
• Add RecvPacket rpc skeleton and associated msg types #7350
• Add Timeout rpc skeleton and associated msg types #7351
• Add Acknowledgement rpc skeleton and associated msg types #7352
• Implement v2 SendPacket rpc handler #7353
• Implement v2 RecvPacket rpc handler #7354
• Implement v2 Timeout rpc handler #7355
• Implement v2 Acknowledgement rpc handler #7356