In this commit, we modify the parsing of user provided outpoints to
ensure that we catch a nil (empty) output early. Otherwise, passing a
set of incorrect arguments would cause `lnd` to crash.
This RPC exposes the recently added BumpFee functionality to the
UtxoSweeper in order to allow users of the RPC to manually bump fees of
low fee inputs/transactions.
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.
