In cases  when a service whants to generate and sign a certificate
it requires a CA key along with a CA cert itself.
For example, Octavia needs it for signing a certificate it generates
for a newly spawned amphora.

This change add sending a CA key to the mine from where it can be
extracted in the cert.sls state.
Also allow managing permissions for a CA cert and key retrieved
from the mine.

Related PROD: PROD-11933

Change-Id: I911effb4a63ae048e348ed04b7aca33998e359aa