allow customising Dockerfile location
As noted in uis/devops/raven/webauth!24, having logan only use a top-level Dockerfile breaks repos which bring their own Dockerfile for deployment as a container.
Update logan to allow overriding docker build options. We copy docker-compose and add an optional "build" section to the configuration which allows overriding the context and dockerfile locations.
Closes #5 (closed)
Edited by Dr Rich Wareham