Add versions to optional dependencies

[paulf81]

This small pull request does two things:

1. Removes the pin on autoyaml put in place in Fix docs #1034 now that the issue is resolved (see YAML compose error in 1.1.2 Jakski/sphinxcontrib-autoyaml#26)

-- Confirm docs build locally

2. Adds versions to optional dependencies as a partial guard against future major version jumps (wouldn't have helped here but good practice!)

[paulf81]

python 3.8 doesn't support the recent major version of pre-commit, I think my preference is to drop 3.8 since it's end of life: https://devguide.python.org/versions/, but we could also give the pre-commit dependency more options,

[misi9170]

My feeling is that dropping 3.8 is appropriate since it is end of life, but @rafmudaf also suggested we could have a more dedicated discussion. Is there also an option to remove tests for 3.8, but not explicitly require that users are at python >= 3.9? What is the usual protocol on that?

[paulf81]

I'm ok with that approach, but it seems it could only be transitory status, where we allow 3.8 but can't guarantee tests pass

[misi9170]

Right. Perhaps that's not good form---perhaps we should strictly require 3.9, I'm not sure.

[paulf81]

that's my vote, since it's end of life it seems that is the right move,

[misi9170]

I've now opened a PR that removes support for python version 3.8 #1042 . Once we are happy with that and it is merged, we can merge develop back into this branch and tests should pass.