SOFTWARE-6168: build external kuantifier

[mwestphall]

• Update GHA to support pulling and building an external git repo via the context, upstream, and upstream_ref fields in build-config.json
• Add support for building to a specific tag rather than {osg_series}-{el}-{repo_name} via the tag field in build-config.json
• Replace large bash script for detecting which image subdirectories have changed with a python script
  • Also, add support for building/pushing to repositories besides opensciencegrid/

Note: Two additional PRs are required in the OSG build/push actions GHAs, since their current versions always git reset --hard the repo prior to build and undo the external repo pull.

• Update push container action to allow skipping the git reset prior to build push-container-action#15
• Add optional input parameter for clean before build build-container-action#13