Do not create a StatefulSet for Arbiters when spec.arbiters is not defined or set to 0.

[verdel]

What did you do to encounter the bug?
Steps to reproduce the behavior:

1. A MongoDB operator is deployed in the Kubernetes cluster.
2. A MongoDBCommunity manifest is created, where spec.arbiters is not specified, and spec.members is set to 1.
3. Two StatefulSets are created in the cluster (one main StatefulSet with replicas = 1 and one for arbiters with replicas = 0).

What did you expect?

If the number of arbiters is not specified or equals 0, an additional StatefulSet should not be created.

• Creating extra objects in the Kubernetes cluster consumes resources in etcd.
• Monitoring systems react to this StatefulSet, as they are configured to report when there is a StatefulSet in the cluster with 0 active replicas.

What happened instead?

Even if we do not specify the need to use Arbiter nodes when creating a MongoDBCommunity, an unused StatefulSet is still created in the cluster, and this behavior cannot be adjusted through additional settings.

Operator Information

• Operator Version (0.11.0)
• MongoDB Image used (mongo:8.0.1)

Kubernetes Cluster Information

• Google Cloud Platform
• Version (v1.28.7-gke.1026000)
• Image Registry location (quay)

Additional context
In the deployStatefulSet function, there is no way to control the creation of a StatefulSet for arbiters. I believe that the part of the code responsible for creating this type of StatefulSet should only execute if spec.arbiters > 0.

If possible, please include:

• The operator logs
• Below we assume that your replicaset database pods are named mongo-<>. For instance:

❯ k get pods
NAME      READY   STATUS    RESTARTS   AGE
mongodb-testing-0   2/2     Running   1 (4d12h ago)   18d                                                                                     

❯ k get mdbc
NAME    PHASE     VERSION
mongodb-testing   Running   8.0.1