Add the ability to manually execute checks against an application

Checks can be run in several ways:

- checks:run APP
- checks:run APP PROCESS_TYPE
- checks:run APP PROCESS_TYPE.CONTAINER_INDEX

This will reuse the existing checks infrastructure as defined by the checks plugin, and therefore if no checks file is defined, it will default to the normal Dokku container check.

Closes #2218

plugins/checks/check-deploy

@@ -53,7 +53,6 @@ checks_check_deploy() {
     local DOKKU_APP_CONTAINER_ID=${DOKKU_APP_CIDS[0]}
   fi
 
-
   # source global and in-app envs to get DOKKU_CHECKS_WAIT and any other necessary vars
   eval "$(config_export global)"
   eval "$(config_export app "$APP")"