Docs/refactors variables topics (#54470) (#54995)

* refactor and partial relref fix

* finishes variables refactor

* Update docs/sources/variables/add-template-variables/index.md

Co-authored-by: Torkel Ödegaard <torkel@grafana.com>

* removes duplicate general options, adds links to general options within tasks

* adds configure variable selection options topic

* starts phase II of refactoring

* incorporates feedback, updates relrefs

* corrects final relrefs

* updates alias

Co-authored-by: Torkel Ödegaard <torkel@grafana.com>
(cherry picked from commit 7147d17567)

docs/sources/visualizations/text-panel.md

@@ -17,4 +17,24 @@ weight: 1100
 
 The text panel visualization lets you make information and description panels for your dashboards.
 
-In **Mode**, select whether you want to use markdown or HTML to style your text, then enter content in the box below. Grafana includes a title and paragraph to help you get started, or you can paste content in from another editor.
+## Mode
+
+**Mode** determines how embedded content appears.
+
+### Markdown
+
+This option formats the content as [markdown](https://en.wikipedia.org/wiki/Markdown).
+
+### HTML
+
+This setting renders the content as [sanitized](https://github.com/grafana/grafana/blob/code-in-text-panel/packages/grafana-data/src/text/sanitize.ts) HTML. If you require more direct control over the output, you can set the
+[disable_sanitize_html]({{< relref "../setup-grafana/configure-grafana/#disable_sanitize_html" >}}) flag which enables you to directly enter HTML.
+
+### Code
+
+This setting renders content inside a read-only code editor. Select an appropriate language to apply syntax highlighting
+to the embedded text.
+
+## Variables
+
+[Variables]({{< relref "../dashboards/variables/variable-syntax" >}}) in the content will be expanded for display.