ContentGuard should be applicable to individual PyPI packages within a distribution/index

Is your feature request related to a problem? Please describe.
There is currently no way to control RBAC permissions on an individual PyPI package within a single pulp_python distribution.

Describe the solution you'd like
There should be a mechanism to apply a ContentGuard to not only a distribution, but also to individual PyPI packages within each distribution.

Describe alternatives you've considered
To try to achieve something similar today, you would need to build 1 distribution and 1 RBACContentGuard per 1 PyPI package to achieve a similar outcome. This will lead to a large # of objects to maintain over time. It will also present a future problem if someone creates a 2nd PyPI package on any existing index, since moving the 2nd package to its own index later would result in a URL change for the 2nd package and may break downstream things that are consuming it. Managing the permissions at the PyPI package level would prevent both of these issues.

No files, tests, or entry points are named. Start by locating how distributions, individual PyPI packages, and ContentGuard/RBAC permissions are represented; done requires a defined, tested mechanism for applying a ContentGuard at package scope without requiring a separate distribution per package.