In this commit, we build on all the prior commits and integrate the new
taproot channels into the existing internal funding flow. Along the way,
we do some refactoring to unify things like signing and verifying
incoming commitment transaction signatures.
For our local nonce, we use the existing functional option type to
derive the nonce based on the initial shachain pre-image we'll use as
our revocation.
This commit adds a new build tag `integration` and removes the old tag
`rpctest` for clarity. Multiple unnecessary usages of `build !rpctest`
is also removed.
With go 1.17 a change to the build flags was implemented:
https://go.googlesource.com/proposal/+/master/design/draft-gobuild.md
The formatter now automatically adds the forward-compatible build tag
format and the linter checks for them, so we need to include them in our
code.
