Document the relaying process for Solana integration

[lumtis]

Describe the Issue

This might have some relationship with https://github.com/zeta-chain/node/issues/2614

For Solana, the TSS signature is not used for the tx per itself, a wrapped tx is created that can be signed by any peer to relay the outbound.

We should do some research and document a proper methodology for relaying:

• Create a new separate process that can be run by anyone to relay all outbounds
• Integration in the ZetaClient (what incentivize you to be the relayer?)
• etc..

[lumtis]

Relaying fully done in ZetaClient for now, removing from the epic