Before that the users had to rely on patching the actual wheel files and
uploading them as different versions to internal artifact stores if they
needed to modify the wheel dependencies. This is very common when
breaking dependency cycles in `pytorch` or `apache-airflow` packages.
With this feature we can support patching external PyPI dependencies via
pip.override tag class to fix package dependencies and/or a broken
`RECORD` metadata file.

Overall design:
* Split the `whl_installer` CLI into two parts - downloading and
extracting.
  Merged in #1487.
* Add a starlark function which extracts the downloaded wheel applies
patches
  and repackages a wheel (so that the extraction part works as before).
* Add a `override` tag_class to the `pip` extension and allow users to
pass patches
  to be applied to specific wheel files.
* Only the root module is allowed to apply patches. This is to avoid far
away modules
modifying the code of other modules and conflicts between modules and
their patches.

Patches have to be in `unified-diff` format.

Related #1076, #1166, #1120