Split Ubuntu 20.04 into Subiquity and Legacy

Allows for transition period on LTS

Closes https://github.com/netbootxyz/netboot.xyz/issues/806

roles/netbootxyz/defaults/main.yml

@@ -528,7 +528,9 @@ releases:
     - code_name: groovy
       name: 20.10 Groovy Gorilla
     - code_name: focal
-      name: 20.04 LTS Focal Fossa
+      name: 20.04 LTS Focal Fossa (Subiquity)
+    - code_name: focal-legacy
+      name: 20.04 LTS Focal Fossa (Legacy)
     - code_name: bionic
       name: 18.04 LTS Bionic Beaver
     - code_name: xenial

roles/netbootxyz/templates/menu/ubuntu.ipxe.j2

@@ -22,7 +22,8 @@ choose ubuntu_version || goto ubuntu_exit
 iseq ${ubuntu_version} older_release && goto older_release ||
 iseq ${ubuntu_version} focal && set install_type sub ||
 iseq ${ubuntu_version} groovy && set install_type sub ||
-iseq ${boot_type} sub && goto boot_type ||
+iseq ${ubuntu_version} focal-legacy && set ubuntu_version focal ||
+iseq ${install_type} sub && goto boot_type ||
 goto mirrorcfg
 
 :older_release