[feature]: create StreamHandler RFQ service (send/recv lnd custom msg)

[ffranr]

Parent issue: #683

In this issue we will add the functionality necessary to subscribe and receive request for quote (RFQ) messages from LND. These messages will be passed between tapd peers via their lnd instances.

This work will involve the creation of a RfqStream component:

This module will use the SendCustomMessage and SubscribeCustomMessages [LND] RPC calls to funnel the RFQ messages (which use the custom message range) to the RfqNegotiator. It should maintain book keeping to keep track of the RfqNegotiator instance for all the active assets the daemon cares about at the time. It'll also need to properly map the requests to responses as well (see the rfq_id value in the messages).

The goal of this issue is to get to a point where we can write integration tests that send and receive RFQ messages via LND.

[ffranr]

I'm going to use 20116 as the custom message type. Index positions of letters "t", "a", and "p" concatenated.

[ffranr]

I noticed that LND sends custom messages with low priority and lazily:
https://github.com/lightningnetwork/lnd/blob/e7687005141701b9a609d12d53a0e84c713370a9/server.go#L4687-L4687

We might want to consider adding message priority customisation to the SendCustomMessage LND RPC endpoint so that we can better ensure timely tap RFQ message exchange.

[ffranr]

Spun out the wire messages into a new issue: #780