fix: implement missing cleanup routines

Without these, there was potential for configuration for certain plugins to continue to exist after an app was deleted.

plugins/docker-options/post-delete

@@ -1,6 +1,7 @@
 #!/usr/bin/env bash
 set -eo pipefail
 [[ $DOKKU_TRACE ]] && set -x
+source "$PLUGIN_AVAILABLE_PATH/docker-options/functions"
 
 trigger-docker-options-post-delete() {
   declare desc="deletes docker options files for an app"