Suffix properties file name with pod name

[solsson]

Because I'd like to explore ways to transition to static configuration, rather than generating config at init. A completely static config would for be more transparent and could, with for example Kustomize's configmap hashes, support rolling updates better.

While investigating if broker ID could be an --override instead I found two blockers:

• Oddly the label that was introduced for statefulsets (after this repo's inception) sets the pod name, not the ordinal.
• Zookeeper needs to be 1-indexed.

I had this comment in code when I was amazed over the design with pod-name instead of pod-ordinal (the former is trivial to create with env expansion):

+++ b/kafka/50kafka.yml
@@ -30,6 +30,9 @@ spec:
         - name: POD_NAME
           valueFrom:
             fieldRef:
+              # Is there any benefit to using this field over metadata.name? fieldPath: metadata.labels['statefulset.kubernetes.io/pod-name']
+              # https://github.com/kubernetes/community/pull/147#issuecomment-350783043
+              # https://github.com/kubernetes/kubernetes/pull/68719 -> new env with fieldPath: metadata.labels['statefulset.kubernetes.io/pod-ordinal']
               fieldPath: metadata.name

It looks like pod-ordinal didn't make it into 1.18.

[solsson]

I added bc2896a because the static files have to be generated with a known number of replicas.

[solsson]

I've also introduced a REPLICAS env. It'll need to be on all zookeeper containers wherever we deviate from the hard coded default scale. It's used to pick a properties file, but also to trigger restart on existing zookeeper pods if you scale up or down. You always have to edit both replicas: and this new env. Previously if you tried to do scale or edit the replicas number you'd get an inconsistent zookeeper setup.

It might be that some of the variants are broken now.

[solsson]

Now part of #311