Recommend the use of pip-system-certs

[Andy-Grigg]

As a result of the issue seen in #637, we are settling on the idea to use pip-system-certs to address this issue, since it essentially does what we would do manually (i.e. look in system pre-defined paths for private CA certificates) but does it automatically by leveraging the system-wide OpenSSL configuration via the python ssl module.

We should decide how we want to do this:

• Include as a dependency of this package
• Include as a dependency of this package in the OIDC extra (since this is when it's actually required, see OIDC authentication fails if Granta MI uses a private cert and the IdP uses a public cert #637), and recommend its use in documentation in other situations
• Only recommend its use and don't install by default at all

The reason for not just including as a dependency in all situations is that it is very side-effect-y, in that it patches all instances of pip and requests at runtime. If a user isn't expecting this then it could be confusing.

Maybe we add it as an additional extra?

@ansys/matbu-project-maintainers Comments welcome on which way to go with this.