Smarter ObjectDiffusion initialisation using a payload on `MsgInit`

[tbagrel1]

Currently, MsgInit has no purpose since it doesn't change the agency (unlike what happens in TxSubmission).

In the future, we think that MsgInit will carry a payload, typically a ticketNo, that allows the outbound side to "resume" from the last known point of the inbound side, instead of advertising any possible object starting with the first one in the database.