[Bug]: RTD page was pointing to version from Oct 2023

[rly]

What happened?

By default, the RTD page https://hdmf-zarr.readthedocs.io/ was pointing to https://hdmf-zarr.readthedocs.io/en/latest which had not been updated since Oct 2023 when the "latest" tag stopped being updated:
https://github.com/hdmf-dev/hdmf-zarr/releases/tag/untagged-2607bb9ce99d67c4e007

I think the term "latest" is ambiguous. Is it the latest release or latest commit? I think we currently use it as latest commit on the dev branch, if it was working as intended. Numpy, pandas, pydantic, and others have adopted the term "dev" for the latest commit on the main branch. I think that's better. There is already an RTD build for the "dev" branch https://hdmf-zarr.readthedocs.io/en/dev/

Plan:

1. Fix the RTD to point to "stable" by default. We could call this "latest" to refer to the latest release instead of the latest commit. Numpy, scipy, pandas, and h5py use the term "stable" in their docs, so I suggest we do the same.
2. I don't think we need a "latest" and "latest-tmp" GitHub release after each commit on the latest dev branch, where the codebase is packaged into an archive. It hasn't been working properly here (the release is filled with every archive instead of just the last one, the title is not updated) and no one has noticed. We could adopt the same policy in HDMF, to remove another moving part and simplify maintenance. Adjust the workflows to make sure this release is not created. RTD auto-builds the "dev" branch already as well.