ci: revamp how we publish documentation

[joanise]

There were several bugs that needed fixing in the docs publication workflow.

New model:

• versions get published as, e.g., v2.0, with the latest version getting alias stable, and alias latest as long as no further commits are done on main
• a push to main triggers the update of dev, with alias latest
• the default is stable, so that docs will default to the documentation of the latest version published to PyPI
• https://roedoejet.github.io/g2p/latest will show the latest, typically dev
• https://roedoejet.github.io/g2p/stable and https://roedoejet.github.io/g2p will show the latest stable
• due to limitations in mkdocs-material, the aliases are not shown in the selector, they only work in URLs.

This PR will require a manual push to gh-pages before it's safe to merge, but afterwards docs updates will be automatic.

[github-actions[bot]]

CLI load time: 0:00.05
PR head 194b8e839ef7adba1a8715133351190a3c1d6d22
Imports that take more than 0.1 s:
import time: self [us] | cumulative | imported package

[joanise]

BTW, the two docs build are not as DRY as ideal, but as I was writing the code to pass the tag and aliases from publish to docs, it turned out that was more complicated and more lines of code than just copy-pasting the checkout/python/dependencies steps from docs.yml to the deploy-docs job in pythonpublish.yml, so I decided that was not worth it.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.23%. Comparing base (cbfd608) to head (194b8e8). Report is 4 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #342 +/- ## ========================================== - Coverage 93.44% 93.23% -0.22% ========================================== Files 18 18 Lines 2334 2334 Branches 516 516 ========================================== - Hits 2181 2176 -5 - Misses 86 90 +4 - Partials 67 68 +1 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.