[feat] docs; update admonition syntax (#68842)

* [feat] docs; update admonition syntax

- Standardizes according to style conventions: https://grafana.com/docs/writers-toolkit/style-guide/style-conventions/#admonitions
- Prepares docs for better, uniform admonition style.

* Remove false positives and irregularities

* false positive removal

* Update docs/sources/datasources/mysql/_index.md

* Update docs/sources/developers/angular_deprecation/angular-plugins.md

* fix link errors

* Prettify some nested blockquotes

* remoe unnecessary admonition

docs/sources/datasources/prometheus/template-variables/index.md

@@ -63,7 +63,9 @@ Regex:
 
 ## Use `$__rate_interval`
 
-> **Note:** Available in Grafana v7.2 and higher.
+{{% admonition type="note" %}}
+Available in Grafana v7.2 and higher.
+{{% /admonition %}}
 
 We recommend using `$__rate_interval` in the `rate` and `increase` functions instead of `$__interval` or a fixed interval value.
 Because `$__rate_interval` is always at least four times the value of the Scrape interval, it avoid problems specific to Prometheus.