Setup cert-manger with letsencrypt

[nce]

Use the official helm chart to deploy the cert-manager.

Configure the ClusterIssuer with letsencrypt

AC:

• [x] cert-manager is deployed in a namespace
• [x] letsencrypt is the default cluster issuer

[tim-tschiersch]

• please add this annotation into every new ingress-object that will be created in the future

  annotations:
    kubernetes.io/tls-acme: "true"