add required job_result_unknown_fmt bot config setting

bot/bot-eessi-aws-citc.cfg

@@ -230,3 +230,4 @@ multiple_tarballs = Found {num_tarballs} tarballs in job dir - only 1 matching `
 job_result_comment_fmt = <details><summary>{summary} _(click triangle for detailed information)_</summary>Details:{details}<br/>Artefacts:{artefacts}</details>
 job_result_details_item_fmt = <br/>&nbsp;&nbsp;&nbsp;&nbsp;{item}
 job_result_artefacts_item_fmt = <li><code>{item}</code></li>
+job_result_unknown_fmt = <details><summary>:shrug: UNKNOWN _(click triangle for detailed information)_<summary/><ul><li>Job results file `{filename}` does not exist in job directory or reading it failed.</li><li>No artefacts were found/reported.</li></ul></details>