Add a UI to rapidly resolve the Elasticsearch cron being 'jammed'.

[Gold]

When setting up Elasticsearch I ended up in an endless loop of "Configure ES (can't, please enable it) > Enable ES (can't, please configure) > repeat". One of these pages had an error referencing cron and there is a note on the Troubleshooting page about it and manually deleting a record in the database did resolve this issue.

This could easily be checked for in code and, if found, a link in the error message could allow the dev/admin to delete this record from the web UI and resolve the issue quickly.

Mahara version: master
OS: Linux (Ubuntu 18.04 LTS)
DB: MySql
Browser: Chromium Version 90.0.4430.72 (Official Build) Built on Ubuntu , running on Ubuntu 18.04 (64-bit)