Dockerfile build-args outline

[grantmacken]

Here is a proposal of what build-args should be provided in the Dockerfile

@ARG VERSION - can be stable or RC e.g. '4.3.1'

• this a requirement of hooks/build, see notes below @ARG BRANCH - branch can be a
  • branch name e.g release,develop, name-of-branch
  • tagged commit e.g. eXist-4.3.1
  • any commit hash ( short or long ) e.g 3b19579, 3b195797a2c2f35913891412859b06d94f189229 @ARG BUILD_DATE @ARG VCS_REF @ARG CACHE_MEM @ARG MAX_BROKER

NOTES: VERSION, BUILD_DATE, VCS_REF build-args are created via a dockerhub build hook in hooks/build CACHE_MEM, MAX_BROKER build args are available, if you want to override the defaults

Build process - build-args provided via docker build are optional.

1. if build-arg VERSION is empty, then version is ignored
2. if build-arg BRANCH is empty then defaults to develop

[duncdrum]

I think this can be closed, no?