Omit storage resource limit if empty (#1637)

We discovered some weird behavior observed on later Kubernetes version (OCP 4.12+)

For some reason why we apply the templates postgres resource with

```
postgres_storage_requirements:
  limit: {}
  requests:
    storage: <x>Gi
```

the `Create Database if no database is specified` task that does the k8s apply will always think the resource is "changed" and proceed to cycle the task and web pod

This resulted in AWX pods being continuously restarted

Update postgres.yaml.j2

roles/installer/templates/statefulsets/postgres.yaml.j2

@@ -33,7 +33,7 @@ spec:
         app.kubernetes.io/instance: 'postgres-{{ supported_pg_version }}-{{ ansible_operator_meta.name }}'
         app.kubernetes.io/component: 'database'
         app.kubernetes.io/part-of: '{{ ansible_operator_meta.name }}'
-        app.kubernetes.io/managed-by: '{{ deployment_type }}-operator' 
+        app.kubernetes.io/managed-by: '{{ deployment_type }}-operator'
     spec:
 {% if image_pull_secret is defined %}
       imagePullSecrets:
@@ -137,7 +137,15 @@ spec:
 {% if postgres_storage_class is defined %}
         storageClassName: '{{ postgres_storage_class }}'
 {% endif %}
-        resources: {{ postgres_storage_requirements }}
+        resources:
+{% if postgres_storage_requirements.limits.storage | default("", true) %}
+          limits:
+            storage: {{ postgres_storage_requirements.limits.storage }}
+{% endif %}
+{% if postgres_storage_requirements.requests.storage | default("", true) %}
+          requests:
+            storage: {{ postgres_storage_requirements.requests.storage }}
+{% endif %}
 
 # Postgres Service.
 ---