[docs] Update docs and wiki in prep for 1.15.0

[johnkerl]

Found while working on issue #2407 / [sc-51048].

There, I need to do a docs audit for the new-shape feature.

I found that many things introduced recently -- including all new spatial classes -- are completely lacking from Python readthedocs content. (The R-side pkgdown material seems complete AFAICT.)

To do on this issue:

• Add all new classes/methods/etc to the manually created .rst files
• Add a new project-level wiki page regarding precisely what needs to be done manually as we all (on the team) do dev work and what is automated
• Incorporate that into our established release procedure. Goal: ensure that all releases include docs for dev work in that release.
• Also notice that 1.15.0rc3 isn't showing up at https://tiledbsoma.readthedocs.io/en/latest/ -- either we need to
  • modify our readthedocs logic to auto-build for RCs, or
  • within our release procedures, show how to manually trigger readthedocs for RCs

[johnkerl]

https://github.com/single-cell-data/TileDB-SOMA/wiki/Branches-and-releases/_compare/68c81d0203c7a37fbb8156b3fa36c18362471c25...25522320fe7cbd29b85a019e371015915d7fb561