Callable workflow for Docker image build

[infotroph]

Description

Fixes #3374 by consolidating the Docker build process into a callable workflow, saving many lines of boilerplate.

Also switches build cache from Docker to GHCR, but does not yet address between-image dependencies that still assume they'll be pulling from Docker -- @robkooper hopefully this gives you an easier starting place for that?

Motivation and Context

Review Time Estimate

• Immediately
• Within one week
• When possible

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• My name is in the list of CITATION.cff
• I agree that PEcAn Project may distribute my contribution under any or all of
  • the same license as the existing code,
  • and/or the BSD 3-clause license.
• I have updated the CHANGELOG.md.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.