Previously only the fee rate used for the last sweep (the sweep bucket
average) was reported. This commit adds the request fee preference to
the report, which is used to select a bucket and the sweep tx fee rate.
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 add a new sub-RPC server to the existing set of gRPC
servers. This new sub-RPC server is the WalletKit. It's a utility
toolkit that contains method which allow clients to perform common
interactions with a wallet such as getting a new address, or sending a
transaction. It also includes some supplementary actions such as fee
estimation.
One thing to note in the RPC file is that we _import_ the existing
signer.proto file in order to get at some existing proto definitions
which are useful in our use case.
