Add summarize_pipeline() function and updates tests

[ryands02]

Adds a helper function, summarize_pipeline(), to better summarize GPA list, plan to add l1/2/3 models' data/big-picture summaries, have not tested compute environment params because we do not have test data that matches the new format.

Also added minimal_gpa list for testing.

[ryands02]

Still need to run build commands to add function export to NAMESPACE and capture documentation.

[wasciutto]

We've added the roxygen documentation, so this is ready for your review @michaelhallquist