Implement CreateOrUpdate in YAMLManager

[eberlep]

Currently, startup of our controllers fails when the Zalando Operator already exist in the cluster:

2020-12-16T15:53:48.126+0100    ERROR   setup   unable to install external YAML {"error": "clusterroles.rbac.authorization.k8s.io \"postgres-operator\" already exists"}

This would easily be recoverable if we would simply update the existing resource instead of exiting.

Also, rolling updates with a newer zalando operator version are not possible without an update?

[LimKianAn]

The current implementation is to create the operator if it doesn't exist. Updating the operator is missing.

[eberlep]

The actual issue was fixed already by splitting the deployment of the CRD and the rest of the operator.

Updating the operator itself will be handled in #106