add support for deterministic entropy

[zoedberg]

In order to use RGB in LN we need to remove any type of entropy in transfers, so that channel counterparties can reconstruct RGB anchors in a deterministic way.

Right now in our rgb-lightning-sample we just duplicated methods with entropy, renamed them in <original_method_name>_static and changed the entropy fields to a fixed number. But ideally, for better privacy, this fixed number should be configurable via the method, so that the channel counterparties can derive this number via some secret channel data.

Here you can see the methods we had to duplicate (dbc_conclude -> dbc_conclude_static and add_raw_state -> add_raw_state_static).

[dr-orlovsky]

Related: #111 (comment)

[zoedberg]

This has been completed, so closing it