Remove Edge, add LTS

Flatcar Edge channel has been retired. A new channel, LTS, has been introduced.

Author: ahrkrak

articles/virtual-machines/linux/flatcar-create-upload-vhd.md

@@ -21,7 +21,7 @@ Linux for each of the Flatcar supported channels:
 - [stable](https://stable.release.flatcar-linux.net/amd64-usr/current/flatcar_production_azure_image.vhd.bz2)
 - [beta](https://beta.release.flatcar-linux.net/amd64-usr/current/flatcar_production_azure_image.vhd.bz2)
 - [alpha](https://alpha.release.flatcar-linux.net/amd64-usr/current/flatcar_production_azure_image.vhd.bz2)
-- [edge](https://edge.release.flatcar-linux.net/amd64-usr/current/flatcar_production_azure_image.vhd.bz2)
+- [LTS](https://lts.release.flatcar-linux.net/amd64-usr/current/flatcar_production_azure_image.vhd.bz2)
 
 This image is already fully set up and optimized to run on Azure. You only
 need to decompress it.