Add NASA HiMAT DEMs

[ShashankBice]

NASA HiMAT produced high-resolution (8m) open-source DEMs from all available DigitalGlobe stereo pairs over the mountains in High Mountain Asia. The team is working on releasing the updated tiled mosaics produced from co-registered DEM strips soon.
The current release contains ~4000 strips, with mosaics obtained from non co-registered DEMs. The new update will add an additional ~2000 strips. I created an issue here to keep track, and will update when the release goes through.

• Link to current release on NSIDC: https://nsidc.org/the-drift/data-update/high-mountain-asia-8-meter-digital-elevation-models-now-available/
• Article detailing processing
• Map showing coverage of the total processed archive of high-resolution DEMs