Use default for replicas

[ansd]

Before this PR, when replicas is not specified, the following error occurs:

error: error validating "cr-example.yaml": error validating data: ValidationError(RabbitmqCluster.spec): missing required field "replicas" in com.rabbitmq.v1beta1.RabbitmqCluster.spec; if you choose to ignore these errors, turn validation off with --validate=false

After this PR, the error does not occur and the default specified in

cluster-operator/api/v1beta1/rabbitmqcluster_types.go

Line 42 in df0c630

// +kubebuilder:default:=1

gets used.

[ferozjilla]

LGTM

[mkuratczyk]

This doesn't really work for me. If you delete these 3 lines https://github.com/rabbitmq/cluster-operator/blob/main/api/v1beta1/rabbitmqcluster_types_test.go#L157-L159 and run make unit-tests, this test will actually fail with RabbitmqCluster.rabbitmq.com "rabbitmq-defaults" is invalid: spec.replicas: Invalid value: "null": spec.replicas in body must be of type integer: "null" while I would expect it to create a single replica instance. Same result when deployed in a real env (I tried 1.17 and 1.18).

[ansd]

@mkuratczyk this is fixed in #405