addon.d now mod v2 compliant to handle A/B devices

Via:
https://gitlab.com/fdroid/privileged-extension/commit/d4a586304806903359312451a3e7eb2ac86fae3c
https://lineageos.org/Changelog-19/#addond-v2

Author: dllud

templates/addond-head

@@ -1,5 +1,7 @@
 #!/sbin/sh
 #
+# ADDOND_VERSION=2
+#
 # /system/addon.d/70-microg.sh
 # During a system upgrade, this script backs up microG apps,
 # /system is formatted and reinstalled, then the files are restored.
@@ -9,4 +11,4 @@
 
 list_files() {
 cat <<EOF
-/etc/permissions/privapp-permissions-microg.xml
+etc/permissions/privapp-permissions-microg.xml