Proposal for new Apache Griffin module

[Chitral Verma <ch...@gmail.com>]

Greetings Griffin dev community.

I wanted to bounce back an idea regarding creation of a new Griffin module,
maybe with the name of "contrib" or "griffin-contrib" which can hold the
extensions (data sources, data sinks, additional measures, etc.) in a
separate module from measure.

Users can use this module as an external plugin passed on the classpath
optionally to access these extensions. Measure module can ship with the
basic Griffin measures and data source support that we currently have.
Implementation for all other external connectors like Elasticsearch,
Cassandra, MongoDB can be moved to the new module along with their
dependencies, test cases etc. This is mostly to avoid bloating of measure
module.

Let me know what you think and based on that I can create a formal GPIP
document.

Regards,
Chitral Verma