feat: add ability to scope retire call to a single app

Also cleanup the log output a bit for the ps:retire command.

docs/development/plugin-triggers.md

@@ -2169,14 +2169,14 @@ CONTAINER_ID="$2";
 
 - Description: Allows you to run scheduler commands when containers should be force retired from the system
 - Invoked by: `dokku run`
-- Arguments: `$DOKKU_SCHEDULER`
+- Arguments: `$DOKKU_SCHEDULER $APP`
 - Example:
 
 ```shell
 #!/usr/bin/env bash
 
 set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
-DOKKU_SCHEDULER="$1";
+DOKKU_SCHEDULER="$1"; APP="$2";
 
 # TODO
 ```