Create a message struct

[atoulme]

Create a message struct from the older testing model:
https://github.com/whiteblock/p2p-tests#message-struct

[adam-hanna]

TBD

https://github.com/agencyenterprise/gossip-host/blob/develop/internal/host/pb/message.proto

[araskachoi]

Will also need to include

• Message type - topic of the message
• Message origin - sending address
• Message destination - receiving address
• Last relaying node - the previous node that sent the message
• Message nonce - chronology of the sent message
• Message size - the message size will be in bytes
• MessageID - unique string associated with that message
• HopCount - number of hops the message had to make in order to reach its destination