♻ (flatpak-sync) Put code in own method

The new method sync is at this point always called

flatpak-sync/flatpak-sync.sh

@@ -9,6 +9,7 @@ set -euo pipefail
 
 APPS_LIST_PATH="${APPS_LIST_PATH:=$HOME/.config/flatpak-sync/apps.list}"
 
+function sync() {
     readarray -t requested_apps < <(cat "$APPS_LIST_PATH")
     readarray -t installed_apps < <(flatpak list --app --columns app | tail -n +1)
 
@@ -33,3 +34,6 @@ for app in "${installed_apps[@]}"; do
             flatpak uninstall -y "$app"
         fi
     done
+}
+
+sync