Add voumes to Dockerfile

[feyst]

Docker recommends to mount volumes instead of mounting directories. This is currently not supported by Borgwarehouse. This is due to some ownership issues. This can be solved by a small change in the Dockerfile.

For example:

...
    volumes:
      - config:/home/borgwarehouse/app/config
      - user-ssh:/home/borgwarehouse/.ssh
      - etc-ssh:/etc/ssh
      - repos:/home/borgwarehouse/repos
      - tmp:/home/borgwarehouse/tmp
      - logs:/home/borgwarehouse/logs

volumes:
  config:
  user-ssh:
  etc-ssh:
  repos:
  tmp:
  logs: