Switch to other serialization format

[adersberger]

• Allow serialization in memory or on disk
• Use Kryo as tried before or use another format like ByteArray or Apache Arrow.

conf.set("spark.serializer", "org.apache.spark.serializer.KryoSerializer"); conf.registerKryoClasses(new Class[]{ MetricTimeSeries.class, MetricObservation.class, MetricDimensions.class, MetricTimeSeriesKey.class, MetricTimeSeriesOrdering.class, FilterObservationByTimestamp.class, ChronixRDD.class, ChronixSparkContext.class, ChronixSolrCloudStorage.class});