refactor: move unimplemented command detection into config file

subcommands/backup-set-encryption

@@ -12,6 +12,7 @@ service-backup-set-encryption-cmd() {
   declare desc="sets encryption for all future backups of $PLUGIN_SERVICE service"
   local cmd="$PLUGIN_COMMAND_PREFIX:backup-set-encryption" argv=("$@"); [[ ${argv[0]} == "$cmd" ]] && shift 1
   declare SERVICE="$1" ENCRYPTION_KEY="$2"
+  is_implemented_command "$cmd" || dokku_log_fail "Not yet implemented"
 
   [[ -z "$SERVICE" ]] && dokku_log_fail "Please specify a name for the service"
   [[ -z "$ENCRYPTION_KEY" ]] && dokku_log_fail "Please specify a GPG encryption key"