Add record container options to ConvertAvroToJSON

ConvertAvroToJSON currently produces a JSON list of the records in an Avro file. There are common alternatives to making a file of JSON records:
1. Concatenating records without the list structure at the root
2. Newline-separating records that contain no newlines in white-space

The processor to convert from JSON to Avro supports those two container options, but not the list of JSON records. It should be easy enough to implement these. I'd also recommend making #2 the default, but that probably isn't possible now that the processor has been released.