refactor: remove need for internal dokku calls

Avoid internal dokku calls will avoid potentially expensive subprocesses - in particular, user-auth will be re-invoked, which can be expensive.

docs/appendices/0.23.0-migration-guide.md

@@ -0,0 +1,5 @@
+# 0.23.0 Migration Guide
+
+## Changes
+
+- The `plugin:list` command no longer outputs the version for the `plugn` binary.

docs/development/plugin-triggers.md

@@ -2108,6 +2108,21 @@ DOKKU_SCHEDULER="$1"; APP="$2"; IMAGE_REPO="$3"; IMAGE_TAG="$4";
 # TODO
 ```
 
+### `storage-list`
+
+- Description: Returns a list of storage mounts
+- Invoked by: `dokku storage:list` and `dokku deploy`
+- Arguments: `$APP`
+- Example:
+
+```shell
+#!/usr/bin/env bash
+
+set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+APP="$1"
+
+# TODO
+```
 ### `tags-create`
 
 - Description: Allows you to run commands once a tag for an app image has been added

docs/getting-started/upgrading.md

@@ -19,6 +19,7 @@ Docker releases updates periodically to their engine. We recommend reading their
 
 Before upgrading, check the migration guides to get comfortable with new features and prepare your deployment to be upgraded.
 
+- [Upgrading to 0.23](/docs/appendices/0.23.0-migration-guide.md)
 - [Upgrading to 0.22](/docs/appendices/0.22.0-migration-guide.md)
 - [Upgrading to 0.21](/docs/appendices/0.21.0-migration-guide.md)
 - [Upgrading to 0.20](/docs/appendices/0.20.0-migration-guide.md)