Add custom metadata to record batches

[rkyleg]

Adding these lines at

arrow-go/arrow/ipc/file_reader.go

Line 490 in 3ae8428

(and replacing line 495) adds the custom metadata to the RecordBatch from the record batches message.

	customMeta, err := metadataFromFB(msg)
	if err != nil {
		panic(err)
	}
	newSchema := arrow.NewSchema(schema.Fields(), &customMeta)
	return array.NewRecordBatch(newSchema, cols, rows)

[zeroshade]

Can you provide an example where the custom metadata isn't preserved? We ostensibly already have tests which confirm that the custom metadata is propagated through IPC (via the integration tests). At a minimum, we should construct a unit test which shows that we're failing to propagate the custom metadata so that we can confirm this will fix it.

Would you be willing to contribute a PR for this?

[rkyleg]

@zeroshade yes, look me work on the unit test and PR

[rkyleg]

closing in favor of #554