DropWizard Parser and Source

[vjkoskela]

Add a new parser implementation for the DropWizard metrics JSON format. Then add a new source implementation that provides reasonable defaults for a DropWizard JSON source.

Reference:

• https://github.com/dropwizard/metrics/blob/4.1-development/metrics-json/src/main/java/com/codahale/metrics/json/MetricsModule.java
• https://github.com/influxdata/telegraf/blob/master/docs/DATA_FORMATS_INPUT.md#dropwizard