Updates needed for mtbs data

[jhamman]

I've noticed a few things with our MTBS dataset that should be corrected:

1. The processed conus and ak 4km datasets are the same (both conus domain)
2. The processed dataset uses a resolution key of 4000 instead of 4000m. This should be updated to match the rest of our catalog conventions.

https://github.com/carbonplan/data/blob/933782082e3a788bed64ecb5541af36919acdef8/catalogs/mtbs.yaml#L35-L39

[freeman-lab]

@jhamman I fixed the 4000 -> 4000m thing in our files and updated the catalog, still need to reprocess ak