Refactor CI jobs

[NicolasHug]

This PR refactors most of our CI job. More refac will probably come later to finalize things.

It's easier to review these few commits individually:

• ed5f8c5 puts our "install pytorch and maybe torchvision" logic in a separate script
• 80aea14 installs test-dependencies in a separate script
• 25e0b77 puts the ffmpeg installation as well as the torchcodec wheel install in separate scripts
• ab32c0c removes docs.yaml to add the doc job as a dependency of the cuda job. This is more efficient: the doc job was building a wheel on its own. But that wheel was already created by the cuda job. The doc job now just depends on the wheel-building part of the cuda job. They still both run in parallel.

The rest of the commits are just attempts at fixing stuff (reordering some steps), which I think you can safely ignore

[Dan-Flores]

I'm curious what effect upgrading this version had? Perhaps we should update the remaining uses of miniconda@v2 in reference_resources.yaml and lint.yaml.