In this commit we add the version 3 htlc, which is implemented with
taproot script spending the two payment paths: the claim path case, and
the timeout case.
TODO - our view etc functions don't have our shared key, find a good way
to get this. A possible solution is just to lazily store it so that we
don't need to call lnd/create a session every time we want to restore
it.
This commit fixes the generation of the htlc address. This bug didn't
affect the swap execution, because the htlc address is only used for
display to the user/caller.