Move exporter options to own sub-category in the ValkeyCluster CRD

[bjosv]

As discussed here #5 (comment) and fixed separately.

Example:

    spec:
      image: valkey/valkey:8.1.3
      shards: 4
      replicas: 2
      exporter:
        image: myname/my-exporter:latest
        resources:
          # ... resources go here