feat(docker): optimize Dockerfile

[duhow]

• builds each dependency in a separate stage, allowing to do parallel build.
• define default value for ARGS, allowing to do docker build local easily.
• do git clone of the specified branch only (depth), getting data faster.
• copy files in a one-off command, reduces the amount of Docker layers created.

Since the files that are most common to change is the build program, having that right at the bottom of the Dockerfile allows to make the other layers reusable.

[mikebrady]

Thanks for this. I'll give it a tryout!

[mikebrady]

Many thanks for this -- it seems a worthwhile improvement!