config objects like `config` and `env` should allow empty/null values

[pgier]

If I set broker.env to an empty/null value the operator crashes. The operator should handle these errors more gracefully.

Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `java.util.LinkedHashMap<java.lang.String,java.lang.Object>` from Array value (token `JsonToken.START_ARRAY`)
 at [Source: (BufferedInputStream); line: 1, column: 6612] (through reference chain: io.fabric8.kubernetes.api.model.DefaultKubernetesResourceList["items"]->java.util.ArrayList[0]->com.datastax.oss.kaap.crds.cluster.PulsarCluster["spec"]->com.datastax.oss.kaap.crds.cluster.PulsarClusterSpec["broker"]->com.datastax.oss.kaap.crds.broker.BrokerSpec["config"])
        at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:59)
        at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1746)
        at com.fasterxml.jackson.databind.DeserializationContext.handleUnexpectedToken(DeserializationContext.java:1520)
        at com.fasterxml.jackson.databind.deser.std.StdDeserializer._deserializeFromArray(StdDeserializer.java:222)
        at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:457)
        at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:32)
        at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:129)
        at io.fabric8.kubernetes.model.jackson.SettableBeanPropertyDelegate.deserializeAndSet(SettableBeanPropertyDelegate.java:134)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:314)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:177)
        at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:129)
        at io.fabric8.kubernetes.model.jackson.SettableBeanPropertyDelegate.deserializeAndSet(SettableBeanPropertyDelegate.java:134)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:314)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:177)
        at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:129)
        at io.fabric8.kubernetes.model.jackson.SettableBeanPropertyDelegate.deserializeAndSet(SettableBeanPropertyDelegate.java:134)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:314)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:177)
        at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer._deserializeFromArray(CollectionDeserializer.java:359)
        at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:244)
        at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:28)
        at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:129)
        at io.fabric8.kubernetes.model.jackson.SettableBeanPropertyDelegate.deserializeAndSet(SettableBeanPropertyDelegate.java:134)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:314)
        at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:177)
        at com.fasterxml.jackson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:323)
        at com.fasterxml.jackson.databind.ObjectReader._bindAndClose(ObjectReader.java:2105)
        at com.fasterxml.jackson.databind.ObjectReader.readValue(ObjectReader.java:1481)
        at io.fabric8.kubernetes.client.utils.Serialization.unmarshal(Serialization.java:253)
        ... 19 more