Docs: Plugins doc reorganization, part 1 (#69864)

* Initial commit

* Prettier fixes

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* Doc-validator fixes part 2

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* Test

* link test

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* fix broken link

* Fix

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* Update docs/sources/developers/plugins/create-a-grafana-plugin/_index.md

Co-authored-by: David Harris <david.harris@grafana.com>

* Testing

* Testing

* Testing

* Testing

* Doc-validator fixes

* Doc-validator fixes

* Doc-validator fixes

* Fix broken links for plugins reorganization project

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* Deleted space

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* Change grafana.com links to absolute URLs for Hugo

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Co-authored-by: David Harris <david.harris@grafana.com>

docs/sources/setup-grafana/set-up-grafana-monitoring.md

@@ -111,7 +111,7 @@ These instructions assume you have already added Graphite as a data source in Gr
 
 ### Pull metrics from Grafana backend plugin into Prometheus
 
-Any installed [backend plugin]({{< relref "../developers/plugins/backend" >}}) exposes a metrics endpoint through Grafana that you can configure Prometheus to scrape.
+Any installed [backend plugin]({{< relref "../developers/plugins/introduction-to-plugin-development/backend" >}}) exposes a metrics endpoint through Grafana that you can configure Prometheus to scrape.
 
 These instructions assume you have already added Prometheus as a data source in Grafana.