Allow configuring NiFi proxy host behaviour

As a user I want to access my deployed NiFi. It has an check that it's own hostname is in an allow-list.

We want to support the following two use-cases:

Turn the check off. Users need this e.g. when they want to deploy the same config to dev, test and prod and are using LoadBalancers because the IPs are not known in advandce.
The user is using an Ingress and knows the NiFi will be reachable at 'nifi.mycorp' and only wants to add this to the allow-list.

We propse the following CRD structure for this:

spec:
  clusterConfig:
    hostHeaderCheck:
      allowAll: true # mandatory, defaults to true
      additionalAllowedHosts: # mandatory, defaults to []
        - nifi-dev.mycorp
        - nifi-test.mycorp
        - nifi-prod.mycorp

### Tasks
- [ ] https://github.com/stackabletech/docker-images/pull/694
- [x] Decide on the default value (@sbernauer: Disable the check by default, as in our Platform all our tools should try to behave the same way in a default config - no other tool has such a silly check!)
- [ ] Implement CRD change in nifi-operator

stackabletech / nifi-operator

Allow configuring NiFi proxy host behaviour #604