[cern] [k8s] Add embed certs to config

cherry-picked from: https://review.openstack.org/#/c/582955/

Add embed certs to kubernetes config file to cluster config

Add option --output-certs to cluster config enabling the output of the
certificates files (ca, key, cert). This is for compatibility with tools
that require the certificates in separate files.

Change-Id: I595d243bc9f30d813af06aad46a9037afe383ab5
Story: 1774643
Task: 21668