Improving sorting / grouping of entries in client configuration documentation

The documentation for Hypothesis [client configuration](https://h.readthedocs.io/projects/client/en/latest/publishers/config.html) has entries sorted in a haphazard fashion, making it harder to find specific settings in the list. It also doesn't do a good job of making it clear which are common options for publishers to want to change (eg. `openSidebar`, `showHighlights`) and which are niche options that have been added for quite specific use cases (especially our LMS app eg. `focus`, `requestConfigFromFrame`).

There is also other cruft in there, such as "experimental" labels on settings that have existed for years and which we're not likely to change soon.