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

[rbcollins123]

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.

[AndersBennedsgaard]

I have set up pull-through caching towards PyPI and wanted to blacklist/whitelist specific packages from PyPI for the users. In this case, it isn't even possible to set up one distribution and content-guard per package