Migrate ITK C++ and Python Github CI procedures into reusable workflows that can be called and run by ITK external modules.

Partially addresses InsightSoftwareConsortium/ITKModuleTemplate#131.

Caveats:

1. Reusable workflows are only designed and tested for simple remote modules with no extra build steps.
2. Passing custom CMake arguments to a remote module build is feasible but untested. Custom CMake arguments should be considered not supported for this first iteration.
3. Remote modules depending on other remote modules or libraries are not currently supported. Modules with extra dependencies are responsible for implementing their own CI pipelines. The workflows here have been forked from ITKModuleTemplate and can in turn be forked as a starting point for a custom pipeline in a remote module repository.