Add support for truststore package

[p-rogalski]

Is your feature request related to a problem? Please describe.

Currently, pdm uses certifi to validate SSL certificates. A custom CA bundle can be passed with pypi.ca_certs for validation of self-signed certificates.

This does not work well on Windows, because the CA bundle is not stored in the filesystem, but in the windows certificate store.

Describe the solution you'd like

Add support for the truststore package, which injects the certificates from the system certificate store into the standard library ssl module.

Pip already added experimental support of truststore behind a feature flag.

Only downside: truststore requires at least Python 3.10, but i guess this could be handled with a simple version check.