Update developer documentation dependencies

[nllong]

Any background context you want to provide?

We were pretty far behind versions in Sphinx. Another PR was failing due to an incompatibility with an older version. Message was The sphinxcontrib.applehelp extension used by this project needs at least Sphinx v5.0; it therefore cannot be built with this version. and seen here

What's this PR do?

• update sphinx
• read in the spelling list so that sphinxcontrib-spelling can use it
• Fix a few documentation errors, there are many more which we can address later.

How should this be manually tested?

• locally run pip install..., tox -e docs

What are the relevant tickets?

n/a

Screenshots (if appropriate)

[github-actions[bot]]

Label error. Requires at least 1 of: Feature, Bug, Enhancement, Maintenance, Documentation, Performance, Do not publish. Found: