Lists with non-primitive members aren't supported in the query string of
a GET request with the current version of the grpc-gateway library. To
allow route_hints to be set through REST, we also offer a POST endpoint
for that call where the encoding of the request parameter can be
specified as JSON.
With the middleware handler in place, we now need to add a new gRPC
interceptor to the interceptor chain that will send messages to the
registered middlewares for each event that could be of interest to them.
The RPC DeletePayment allows deleteing single payment from its ID. When calling with `FailedHtlcsOnly` set in the request only failed HTLCs of this payment will be deleted.
To avoid a naming conflict with etcd, we rename our very generic
rpc.proto to lightning.proto to match the service name that's declared
within. This will break many external tutorials and possibly also our
API docs but the change needs to be done eventually.
