Support building from sdist as a build action instead of repository_rule.

Things needed:

• A way to use a different repository rule that would not do any building with pip.
• Parsing the dependencies from pyproject.toml so that the deps field is populated at the repository time.
• A pip toolchain or something similar for building packages. Maybe we should have a toolchain for each build backend in the https://peps.python.org/pep-0621/
• A way to specify build dependencies see pip_parse: lockfile for build dependencies in repository rule #1325.
• How do we build Python extensions?

Initial thoughts:

• It would be good to create an sdist_archive rule, which would download a given sdist by URL and then would parse pyproject.toml. If the pyproject.toml is not found or it is dynamic and requires Python to correctly infer the dependencies, we may need to fail at least in the first iteration.
• Using Python in the repository context is OK, but adds a lot of complication in the long run - we should attempt to limit its usage as much as possible.

At the moment I don't have time to work on this myself, but writing it down so that an issue for PEP621 based sdist building exists. Feel free to add thoughts here on possible design.