New section on filtering and search (CCC)

Filtering and search for Childhood Cancer Collections will differ from the filtering and search refine.bio currently supports, as it will be "powered" by ontological terms. This issue tracks adding a section on how CCC filtering and search will function.

It should cover the following:

* Filtering by ontological terms
* How hierarchical ontological search works
* How samples table filtering works

No file, test, or entry point is named. Start by locating the existing refine.bio filtering and search documentation and the CCC behavior, then add a section covering ontological-term filtering, hierarchical ontological search, and samples table filtering.

Written by the indexing model from the issue text.