refactor(pypi): move config setting processing to the macro

[aignas]

Before hand we would pass around whl_alias struct instances and it
would go through rounds of starlark functions which would end up
rendered as BUILD.bazel files in the hub repository. This means that
every time the output of the said functions would change, the
MODULE.bazel.lock would also possibly change.

Since we now have much better unit testing framework, we start relying
on these functions being evaluated at loading phase instead of repo rule
phase, which means that we can make the BUILD.bazel files not change a
lot when the underlying code changes, this should make the code more
maintainable in the long run and unblocks the code to accept extra
things, like env marker values or similar.

Summary:

• Remove the repo field from whl_alias.
• Rename whl_alias to whl_config_setting
• Move the tests around
• Simplify the pkg_aliases tests to use contains instead of exact
  equality to make things less brittle.
• Simplify the pkg_aliases tests to use different mocks to make
  expectations easier to understand.
• Make whl_config_setting hashable by using tuples instead of lists.
• Adjust how we store the whl_config_setting in the PyPI extension
  and optimize the passing to the hub_repository.

This is needed for #2319 and #2423.

To be in future PRs:

• Remove the need to pass osx_versions, etc to the pkg_aliases macro.

[aignas]

I need to revisit the error message wording here. Will do later.