In this commit, we create a new chainfee package, that houses all fee
related functionality used within the codebase. The creation of this new
package furthers our long-term goal of extracting functionality from the
bloated `lnwallet` package into new distinct packages. Additionally,
this new packages resolves a class of import cycle that could arise if a
new package that was imported by something in `lnwallet` wanted to use
the existing fee related functions in the prior `lnwallet` package.
In this commit, we address an issue that would cause us to scan from the
genesis block for the spend of an output that we wish to use to raise
the fee of a transaction through CPFP. This was due to setting a 0
height hint when constructing the input required by the sweeper and was
discovered due to the recently added validation checks at the chain
notifier level. We'll now use the current height as the height hint
instead as the sweeper will end up creating a new transaction that
spends the input.
In this commit, we implement the newly defiend WalletKitServer gRPC
service. We use the same template w.r.t build tags as the existing
signrpc service.
