refactor: move unimplemented command detection into config file

subcommands/backup

@@ -13,6 +13,7 @@ service-backup-cmd() {
   declare desc="creates a backup of the $PLUGIN_SERVICE service to an existing s3 bucket"
   local cmd="$PLUGIN_COMMAND_PREFIX:backup" argv=("$@"); [[ ${argv[0]} == "$cmd" ]] && shift 1
   declare SERVICE="$1" BUCKET_NAME="$2" USE_IAM_OPTIONAL_FLAG="$3"
+  is_implemented_command "$cmd" || dokku_log_fail "Not yet implemented"
 
   [[ -z "$SERVICE" ]] && dokku_log_fail "Please specify a name for the service"
   [[ -z "$BUCKET_NAME" ]] && dokku_log_fail "Please specify an aws bucket for the backup"