This commit bumps LND and lndclient to make it possible to upgrade
taproot HTLC construction with a MuSig2 version. This is required to
support both old (MuSig2 0.4) and new (MuSig2 1.0) clients.
In this commit we bump the minimum LND version required to run loopd to
v0.15.1-beta in order to ensure that the underlying chain backend
supports taproot (https://github.com/lightningnetwork/lnd/pull/6798)
We need the newer version of lndclient to get our synced to chain
state. This requires changes to our test mock, so it is separated
into a different commit. Since lndclient is expanding to be used in
projects other than loop, the client interface is embedded in our
mock rather than implementing functions we do not need. Functions that
we already use in tests are updated accordingly.
Note that while this commit bumps us to a version of lndclient that
defaults to requiring lnd 0.11, we do not bump our required version
yet because we are not using any new endpoints.
