Evaluate trust-manager to replace renku/certificates

[sgaist]

Currently, renku uses the renku/certificates image to dispatch updated certifcates to the sessions and other components. While this is working, it requires regular updating of the image in order to ensure the latest version of the CA certificates are in use.
The cert-manager team has created trust-manager which goal is to allow for an easy way to serve custom certificate bundles to workload.

This ticket tracks the work to evaluate it as a replacement for the certificates image.