feat: add support for cert-manager for etcd tls secrets

[boebu]

This PR introduces the option to hand TLS certificate handling to cert-manager by adding the required configuration in helm values:

certManager:
  # -- Enable CertManager for etcd certificates
  enabled: true
  # -- CertManager Issuer to use for the etcd certificates
  issuerRef:
    name: kamaji-etcd-issuer
    kind: ClusterIssuer
    group: cert-manager.io
  # -- CertManager etcd CA validity
  ca:
   validity: 87600h # 10 years

Since etcd supports per-connection TLS reload automatic rotation works without any intervention, except for the CA. CAs must be rotated as of today with a semi-automatic process which includes a rollout restart of all components.

[prometherion]

@boebu unfortunately, we have some conflicts: may I ask you to get those fixed so we can merge this too, please?

[boebu]

@boebu unfortunately, we have some conflicts: may I ask you to get those fixed so we can merge this too, please?

Conflicts are resolved, is there anything left from your pov?