Expose Redpanda behind a single NLB

[EladDolev]

For exposing Redpanda behind a single NLB, a few configurations need to be added to the CRD
This can be used (among other things) to expose Redpanda cluster via PrivateLink Service Endpoint. An idea for that can be seen here

In order of achieving it, need be able to expose the brokers with a per-broker NodePort, together with another NodePort for the bootstrap address.
Target group would be created per broker, and for the bootstrap address.
The advertised ports per broker, would be added as listener rules on the NLB.
The easiest way is if all brokers advertise the same hostname, and that hostname is being added as a DNS record to point to the NLB.

One approach, for maximum flexibility, would be having configurations for the bootstrap service, and per-broker configuration as the Strimzi operator does it

spec:
  {{- with .Values.kafka }}
  kafka:
    replicas: {{ .replicas }}
    listeners:
      external:
        type: nodeport
        overrides:
          bootstrap:
            nodePort: {{ .basePort }}
          brokers:
          {{- range until (int .replicas) }}
          - broker: {{ . }}
            nodePort: {{ $.Values.kafka.basePort | add . | add 1 }}
            advertisedHost: {{ $.Release.Name }}.{{ $subdomain }}
            advertisedPort: {{ $.Values.kafka.basePort | add . | add 1 }}
          {{- end }}
.
.
.
  {{- end }}

Another approach can be just specifying the advertisedHost and basePort and the operator would create a NodePort for each broker as basePort + <broker number> and use the same port as the advertisedPort

Would appreciate your thoughts for what approach is better, and how the CRD should look like to accommodate those changes.

[emaxerrno]

@EladDolev thanks for the idea. Tagging @alenkacz @dimitriscruz @RafalKorepta