In this commit, we add the state transitions for the new protofsm based
RBF chan closer. The underlying protocol is a new asymmetric co-op close
process, wherein either side can initiate a chan closer, and use their
settled funds to pay for fees within the channel.
In this commit, we add the initial set of states for the new protofsm
based rbf chan closer. A diagram outlining the new states and their
transitions can be found here:
https://gist.github.com/Roasbeef/acc4ff51b9dff127230228a05553cdfe.
Unlike the existing co-op close process, this co-op close can be
restarted at anytime if either side sends a shutdown message. From
there, we'll each obtain a new RBF'd version that can be re-broadcasted.
This commit creates the set of states, along with the environment that
our state machine will use to drive itself forward.
