Improve Zot dashboard (#505)

* Make variables refresh on time range change

* Restrict PVC query to zot namespace

* Add datasource variable

* Use templated datasource variable

* Specify namespace for stat query, use table instead of series

* Set some descriptions

* Set some units

* Add data transfer panel

* Add descriptions and tweak details

* More tweaks

* Update CHANGELOG.md

* Fix "Download rate" panel query

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- Improved many details on the dashboard "In-cluster container registry (Zot)".
 - Change `net-exporter` dashboard ownership from turtles to cabbage.
 - Change `cluster-total.json` dashboard ownership from turtles to cabbage.
 - Change `namespace-by-pod.json` dashboard ownership from turtles to cabbage.