Add TLS manager to automatically generate, store and renew CAs #744

The TLS manager keeps track of the existing TLS CAs and certs and renews/rotates them when they are about to expire.
You can request the currently valid certificate from the TLS manager.

Add a TLS manager which manages multiple CAs and rotates them if necessary. Followup of #736.

There is already a similar module in the secret-operator that can be used as a reference when implementing this.