Add source plug-in for CHOP's Clinical Pathways Library

It was suggested to add support for the Clinical Pathways Library at the Children's Hospital of Philadelphia. This is an interesting source given that it is mostly flowcharts (in HTML). The indexer would have to make sense of the flowcharts somehow - it's not simply a straight crawl & index.

https://www.chop.edu/pathways-library

Many clinical libraries are similar in that they operate with flowcharts as the main content. This source plugin would provide an example.

Start by examining the CHOP Clinical Pathways Library at https://www.chop.edu/pathways-library and determine how its HTML flowcharts should be represented for indexing. Review the repository's existing crawler or source-plugin entry points, then define completion as a working plugin that indexes this library and demonstrates an approach applicable to similar clinical flowchart sources.

Written by the indexing model from the issue text.