feat: add report trigger

This allows users to quickly show the state of any configured application, as well as the state of their server. In doing so, we make it easy for them to provide information necessary for debugging in a single command.

docs/development/plugin-triggers.md

@@ -1105,6 +1105,22 @@ APP="$1"; HOSTNAME=$(hostname -s)
 mail -s "$APP containers on $HOSTNAME failed to retire" ops@example.com
 ```
 
+### `report`
+
+- Description: Allows you to report on any custom configuration in use by your application
+- Invoked by: `dokku report`
+- Arguments: `$APP`
+- Example:
+
+```shell
+#!/usr/bin/env bash
+
+set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+APP="$1";
+
+# TODO
+```
+
 ### `scheduler-deploy`
 
 - Description: Allows you to run scheduler commands when an app is deployed