feat(kb/gatus): start article about gatus

knowledge base/gatus.md

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+# Gatus
+
+Health dashboard.
+
+It allows to monitor services using HTTP, ICMP, TCP, and DNS queries.<br/>
+One can evaluate the result of said queries by using a list of conditions on values (like status code, response time, certificate expiration, body and many others).
+
+Each health check can be paired with alerting via Slack, Teams, PagerDuty, Discord, Twilio and many more.
+
+1. [TL;DR](#tldr)
+1. [Further readings](#further-readings)
+   1. [Sources](#sources)
+
+## TL;DR
+
+## Further readings
+
+### Sources
+
+- [Github]
+
+<!--
+  References
+  -->
+
+<!-- In-article sections -->
+<!-- Knowledge base -->
+<!-- Files -->
+<!-- Upstream -->
+[github]: https://github.com/TwiN/gatus
+
+<!-- Others -->