Create in-memory use case for enrichment with map type and flatfile summarizer

We should be able to use the flatfile summarizer to create a serialized representation of a map, store that representation in HDFS, and use it for in-memory enrichments. The first pass would be a 1-time static load. Future enhancements to the use case and Stellar functions could include a backing cache that reloads the enrichments and enables a streaming enrichment-like capability.

https://github.com/apache/metron/tree/master/metron-stellar/stellar-common#object_get

https://github.com/apache/metron/tree/master/metron-platform/metron-data-management#flatfile-summarizer