Add reader for GEO-KOMPSAT AMI

[djhoese]

There has been interest in creating a reader for the new AMI instrument onboard GEO-KOMPSAT-2A satellite (GEO-KOMPSAT-2B in the future). @rayg-ssec has mentioned it as a possible task for him during the Pytroll Contributor Week. He has been one of the primary decoders of the format here at the SSEC so it would be great to get some initial help from him on this.

The instrument is very similar to ABI and AHI, but the format is very different from both. Platform name should probably be "GEO-KOMPSAT-2A" to match OSCAR: https://www.wmo-sat.info/oscar/instruments/view/285

Github won't let me assign Ray, but let's consider him assigned until stated otherwise.

[djhoese]

@rayg-ssec Started a python module for reading the data (outside of Satpy) here: https://gitlab.ssec.wisc.edu/rayg/himawari/blob/feature-gk2a-ami/himawari/ami2cmi.py

Not sure if this is public, but I can see it.