Add documentation about embedding Markdown content into Grafana

[amotl]

About

Based on Grafana's Text Panel, we added a snippet to load Markdown from Apicast's HTTP API into Grafana.

References

• Example dashboard: HTML and Markdown embedding
• https://community.hiveeyes.org/t/markdown-inhalte-im-grafana-einbetten/4941
• [markdown-remote] Rendering Markdown fetched from a remote location, with interval-based refresh and cache busting grafana-toolbox/grafana-snippets#2

Backlog

Other than linking to those resources, two details need to be added to the documentation. First, a CORS header needs to be added to the HTTP endpoint which serves Apicast's API. This configuration directive for Nginx would be suitable.

add_header Access-Control-Allow-Origin *;

In order to be able to run JavaScript within the HTML mode of Grafana's Text Panel, it needs to be configured with disable_sanitize_html in /etc/grafana/grafana.ini.

[panels]
disable_sanitize_html = true