This commit adds a new FlagTaprootChannel Flag which is then used to
construct a new blob Type: TypeAltruistTaprootCommit. New watchtower
feature bits are also added (4/5).
In this commit a new enum, CommitmentType, is introduced and initially
there are 3 CommitmentTypes: Legacy, LegacyTweakless and Anchor.
Then, various methods are added to `CommitmentType`. This allows us to
remove a bunch of "if-else" chains from the `wtclient` and `lookout`
code. This will also make things easier to extend when a new commitment
type (like Taproot) is added.
In this commit, we add an Identifier method to the blob.Type struct
which returns a unique identifier for a given blob type. This identifier
is then used for initialising the disk overflow queue of the given
client.
Adds flags for reward outputs and commitment outputs.
The fixed-size encoding for commitment outputs is
treated as a flag, so that the blob format can be
modified, extended, or replaced in future iterations.
