Cerbos git storage fail knownhosts key mismatch ssh

## What happened

Cerbos with the git storage driver (protocol ssh, cloning from github.com) fails to start with a `knownhosts: key mismatch` error. The SSH known_hosts inside the container does not match GitHub's current host keys.

## The fix that worked

Populate the container's known_hosts from ssh-keyscan before Cerbos starts: create a ConfigMap with the output of `ssh-keyscan github.com` and mount it at /etc/ssh/ssh_known_hosts for all Cerbos pods (or do the same in an init container). The reporter confirmed this fixed the clone failure. Also make sure any old cached host keys are cleaned up if GitHub has rotated keys since the image was built.