In this commit, we modify all sub-servers as well as the main lnd gRPC
service to use a macaroon per call rather than a connection level
macaroon. The old approach would result in us using the same macaroon
for the entire connection, while this new approach allows us to use
multiple macaroons with a single connection.
We move to this new approach as it doesn't require users to delete their
admin macaroon before being able to use Loop. It also preps us for a
future where there is no admin macaroon, and we instead need to use a
set of macaroons to accomplish our tasks.
In this commit, we modify the `NewLndServices` method to accept the
directory where macaroons are stored, rather than the path for the admin
macaroon. This is a prep to moving towards a multi-macaroon system, as
the `macaroonPouch` will handle storing the various macaroons.
In this commit, we add a new struct, the `macaroonPouch`. This struct
bundles all the macaroons we need for each sub-server. Along the way, we
also export the set of default* paths for lnd, and add a new set of
variables that store the default file names of each of the macaroons for
each sub-server.
The `WithMacaroonAuth` method on the `serializedMacaroon` type will
allow us to attach a macaroon for each call rather than attaching it at
the connection level. This slight change will allow us to use multiple
macaroons over a single RPC connection, rather than a single global
macaroon.
