doc: document current_cc_headers and related targets

This is a ticket to document the targets in https://github.com/bazel-contrib/rules_python/blob/cab415d82ebbfd1b8b2d81ef61baf3f9a274a1b2/python/cc/BUILD.bazel#L15 and other in the same file so that we can point users to documentation on how to use toolchain lookup instead of the legacy alias targets in toolchain repos that we are still creating.

Maybe this ticket can also document similar targets for the python toolchain as well.

EDIT: Looked at the docs again and I see that the easiest way to document this would be to add a sentence or two in https://rules-python.readthedocs.io/en/latest/toolchains.html#python-c-toolchain-type so that the users know how to consume headers and `libpython`.

Cross-referencing https://rules-python.readthedocs.io/en/latest/toolchains.html#local-toolchain with `seealso` to the `python-c-toolchain-type` would be also useful.

Lee los targets de python/cc/BUILD.bazel y, después, revisa toolchains.html en las secciones “python-c-toolchain-type” y “local-toolchain”. Documenta cómo los usuarios consumen headers y libpython mediante la búsqueda de toolchains, y añade la referencia cruzada seealso sugerida; aclara si también deberían cubrirse targets similares de Python toolchain.

Escrito por el modelo de indexación a partir del texto del issue.