feature request: add support for tor HashedControlPassword authentication

[lesinigo]

TL;DR

Having support for HashedControlPassword authentication to the tor control port would be useful. The MESSAGING:onion section could have a new tor_control_password setting and use that if present or fall back to Cookie based auth if the setting is missing or empty.

rationale

The onion message channels currently support only Cookie based authentication, precluding (or, technically, making it much more difficult) to use a tor service running on another host / vm / container.

There could be a number of reasons to not want to have tor running alongside JoinMarket, in my case I want to have a number of services, like a bitcoin full node, a joinmarket yield generator, etc... running in isolated containers without any access to internet because I want all my traffic to go over tor.

This leads to these two issues:

1. when there are other services that need to use tor, running in other systems / containers, it would be a waste for every one of them to have its own tor, they could all use a single tor accessed over the network
2. if the services are supposed to only talk to the external world over tor, the network where services run would not have internet access (eg. no router / gateway) to enforce that policy. A dual-headed system / container could run tor, listening for connection over one network and accessing internet over a second network

For an actual example, my setup is using a docker-compose.yml along these lines:

---
networks:
  wan:
    # this has internet access
  tor:
    # no internet access
    internal: true

services:
  tor:
    networks:
      - wan
      - tor
  bitcoin:
    # the full node
    networks:
      - tor
  joinmarket:
    # could be a tumbler (uses tor but doesn't need auth to control port)
    # or yield generator (does need to authenticate with tor control port)
    networks:
      - tor