Replace check.sh and/or ci.sh with tox/nox

[jakkdl]

Tox sounds wonderful. I've been meaning to suggest it. I've actually been working on some reusable workflows for tox-based projects + experimented with some cool GHA integrations.
When you get to it, I may offer some help / experimentation in simplifying things here.

Originally posted by @webknjaz in #3157 (comment)

thread contains more discussion on tox vs nox. Whoever wants to Do It can probably just decide on either.

Initial PR does not need to be a huge one that replaces all of check.sh & ci.sh and overhauls CI stuff, an incremental approach should work perfectly fine here.

[webknjaz]

Reopening #3196 because it says that it's not enough right in the first sentence.. It's the close keyword that's at fault.

[jakkdl]

followup from #3196 (comment): remove quotes from descriptions

[webknjaz]

followup from #3196 (comment): remove quotes from descriptions

And the descriptions can be multi-line + contain substitutions like {basepython} which would make the expanded env definitions even more distinctive.
Example: https://github.com/ansible/awx-plugins/blob/b90483b/tox.ini#L225C3-L230C77.

[webknjaz]

Another follow-up (#3196 (comment)): call tox from RTD.

Example: https://github.com/ansible/awx-plugins/blob/b90483b/.readthedocs.yaml + https://github.com/ansible/awx-plugins/blob/b90483b/tox.ini#L372C7-L372C53.

[webknjaz]

And another one (#3196 (comment)): separate tox invocation into installing the deps and running the (test) commands.

Example: https://github.com/ansible/awx-plugins/blob/b90483b/.github/workflows/reusable-tox.yml#L288-L301 (tox r --notest -vvv) + https://github.com/ansible/awx-plugins/blob/b90483b/.github/workflows/reusable-tox.yml#L312-L327 (tox r --skip-pkg-install -q).

Bonus points for an additional tox invocation with maximum verbosity, rerunning the failed tests, also with maximum verbosity of pytest: https://github.com/ansible/awx-plugins/blob/b90483b/.github/workflows/reusable-tox.yml#L366-L382 + https://github.com/ansible/awx-plugins/blob/b90483b/.github/workflows/ci-cd.yml#L699-L702.