Added OMPS AI descriptions; created AI category

[minniewong]

Description

Fixes nasa-gibs/worldview#1305.

Added 2 descriptions - OMPS Aerosol Index and OMPS Aerosol Index (PyroCumuloNimbus); created an Aerosol Index measurement (moved the AI layers out of the AOD measurement)

Checklist

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@nasa-gibs/worldview

[ZachTRice]

👍