Graceful handling of null typed avro fields

[devinrsmith]

Consider a "null" typed avro field (likely as a subfield of a record):

 {
   "name": "my_null_field",
   "type": "null",
   "default": null
 }

While it may seem strange at first, this construction may allow the caller to explicit force a digest-bump for changes that would otherwise not change the digest; for example, if documentation of a field changed, or an aliased was added or changed, it might be nice to force a digest bump. In this case, the caller could "rename" this field ("rename" in this case is really removing a field and adding a field from the perspective of avro):

 {
   "name": "my_null_field_v2",
   "type": "null",
   "default": null
 }

While the following is a stacktrace that includes an enterprise component, we should investigate how the core natively handles this situation (both consuming and producing).

io.deephaven.engine.table.TableDefinition$IncompatibleTableDefinitionException: Table definition incompatibilities: 
	Kafka table column 'my_null_field' is missing in on-disk (Kafka.BaseValuation)
	at io.deephaven.engine.table.TableDefinition.checkMutualCompatibility(TableDefinition.java:395)
	at io.deephaven.enterprise.kafkawriter.KafkaTableWriter$Registrar.register(KafkaTableWriter.java:1041)
	at io.deephaven.kafka.KafkaTools$KafkaRecordConsumerFactoryCreator.lambda$visit$3(KafkaTools.java:1169)
	at io.deephaven.kafka.ingest.KafkaIngester.lambda$new$5(KafkaIngester.java:222)
	at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183)
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197)
	at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:179)
	at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1625)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
	at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150)
	at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:596)
	at io.deephaven.kafka.ingest.KafkaIngester.<init>(KafkaIngester.java:220)
	at io.deephaven.kafka.KafkaTools.consume(KafkaTools.java:1262)

https://avro.apache.org/docs/1.11.1/specification/_print/#transforming-into-parsing-canonical-form