Install ext-theme from requirements.txt

[humitos]

Move this Python package into our requirements workflow.

Closes #12140

[stsewd]

Won't this affect production? We will be installing the latest version available on main instead of the version from the release.

Also, does this still allow us to hot reload locally? Like the changes from the local copy are taken into effect when running .org or .com locally

[ericholscher]

Yea, we should probably at least use a rel branch here, to ensure static releases. But I don't think this PR changes that in any way? We were already installing from main

[humitos]

I think both are correct here. We were installing from rel on production, but from main in development.

I kept the installation for development inside Dockerfile and I put the readthedocsext-theme package on those requirements where it's needed (testing, deploy)

Please, take another look and let me know. By the way, the PR that removes the Salt states is at https://github.com/readthedocs/readthedocs-ops/pull/1662

[ericholscher]

This seems reasonable to me. Just to confirm, this doesn't change how we do it in Docker, where it's using a local mount, right?

[humitos]

Just to confirm, this doesn't change how we do it in Docker, where it's using a local mount, right?

Yeah, we are not changing that.

[stsewd]

What about .com? We need to install from relcorp there.