Implement IBC message builder components for Sovereign rollup

[soareschen]

It is rather straightforward to implement the IBC message builder components for Sovereign rollup, as they are pretty similar to the message builder implementations for Cosmos-to-Cosmos.

The main differences are:

• A dummy signer field is used, by calling Signer::dummy().
  • cc @farhard: it is possible to make it such that IBC message types for sovereign-ibc do not include this field at all? Or should the proper signer be used eventually?
• The message is encoded into Any, and wrapped inside SovereignMessage.

Assignees can use the following implementations as reference:

• BuildCreateCosmosClientMessageOnSovereign for CreateClientMessageBuilder<SovereignChain, CosmosChain>.
• BuildUpdateCosmosClientMessageOnSovereign for UpdateClientMessageBuilder<SovereignChain, CosmosChain>

Tasks

• ConnectionHandshakeMessageBuilder<SovereignChain, CosmosChain>
  • Part of Implement connection handshake between Sovereign and Cosmos #245
  • Fill in the todo!() for BuildCosmosConnectionHandshakeMessageOnSovereign
• ChannelHandshakeMessageBuilder<SovereignChain, CosmosChain>
  • Part of Implement channel handshake between Sovereign and Cosmos #246
  • Fill in the todo!() for BuildCosmosChannelHandshakeMessageOnSovereign
• ReceivePacketMessageBuilder<SovereignChain, CosmosChain>
  • Part of Implement ReceivePacket relaying from Cosmos to Sovereign #274
• AckPacketMessageBuilder<SovereignChain, CosmosChain>
  • Part of Implement AckPacket relaying from Cosmos to Sovereign #277
• TimeoutUnorderedPacketMessageBuilder<SovereignChain, CosmosChain>
  • Part of Implement TimeoutUnorderedPacket relaying from Cosmos to Sovereign #279

[seanchen1991]

To clarify, is the scope of this work implementing something like the following components?

• BuildCreateIBCClientMessageOnSovereign for CreateClientMessageBuilder<SovereignChain, IBCChain>
• BuildUpdateIBCClientMessageOnSovereign for UpdateClientMessageBuilder<SovereignChain, IBCChain>

[soareschen]

The listed components are already implemented, and are for your reference. By "IBC message builders" I mean message builder for IBC-related messages, such as ReceivePacketMessageBuilder.

You can implement new components such as:

struct BuildReceivePacketMessageOnSovereign;

impl<Chain, Counterparty> ReceivePacketMessageBuilder<Chain, Counterparty>
  for BuildReceivePacketMessageOnSovereign
where
  ...

[seanchen1991]

Looking at the constraints for BuildCosmosReceivePacketMessage, I'm not entirely sure which constraints needs to change for BuildReceivePacketMessageOnSovereign. More specifically, for the Chain: HasMessageType constraint, what should the Message associated type be set to?