Expand `kudo get` command

[ANeumann82]

What this PR does / why we need it: Extends the kudo get command. It now supports

• Get "instances", "operators", "operatorversions" and "all".
• --output yaml or --output json

Examples:

kudo get all

List of current installed operators including versions and instances in namespace "default":
.
└── some-operator
    └── some-operator-0.1.0
        └── test

kudo get operators --output yaml

---
apiVersion: kudo.dev/v1beta1
kind: Operator
metadata:
  creationTimestamp: null
  name: some-operator
  namespace: default
spec:
  description: A fancy Operator
  kudoVersion: 0.16.0
status: {}

...

Fixes #556, #331