In this commit, we add support for the new musig2 channel funding flow.
This flow is identical to the existing flow, but not both sides need to
exchange local nonces up front, and then signatures sent are now partial
signatures instead of regular signatures.
The funding manager also gains some new state of the local nonces it
needs to generate in order to send the funding locked message, and also
process the funding locked message from the remote party.
In order to allow the funding manger to generate the nonces that need to
be applied to each channel, then AddNewChannel method has been modified
to accept a set of options that the peer will then use to bind the
nonces to a new channel.
