Merge branch '159-add-jitsi-to-list-of-custom-apps' into 'main'

Resolve "Add Jitsi to list of custom apps"

Closes #159

See merge request !137

frontend/public/custom/markdown/jitsi.md

+---
+title: 'Jitsi'
+tileExcerpt: 'Secure and flexible video conferencing'
+---
+
+## Introduction
+
+> Go ahead, video chat with the whole team. In fact, invite everyone you know. Jitsi Meet is a fully encrypted, 100% open source video conferencing solution that you can use all day, every day, for free — with no account needed. (from the [official website](https://jitsi.org/jitsi-meet/))
+
+## Signing in
+
+Jitsi does not require logins; every video session is end-to-end encrypted and is only visible to people currently on the call.