EMC_post repository name change to UPP

[fossell]

The post processing repository has changed the name from EMC_post to UPP to be consistent with other naming conventions across the board. Need to update the Externals.cfg file to use new naming convention. Other mods may be needed depending on how the app build works with this external repo.

[UPP]
tag = ufs-v1.1.0
protocol = git
repo_url = https://github.com/NOAA-EMC/UPP.git
local_path = src/upp
required = True