Docs: Remove old plugin docs, fix URLs to go to new dev portal (#75325)

* Remove old plugin docs, add redirects to new dev portal

* Restore plugin.schema.json file

* Update docs/sources/administration/plugin-management/index.md

Co-authored-by: Jack Baldry <jack.baldry@grafana.com>

* More updates

* Cleanup links

* Update docs/sources/alerting/fundamentals/evaluate-grafana-alerts.md

Co-authored-by: Jack Baldry <jack.baldry@grafana.com>

* fix codeowners

* Change reference links to inline links to avoid 404s

* Update docs/sources/datasources/_index.md

Co-authored-by: Jack Baldry <jack.baldry@grafana.com>

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

Co-authored-by: Jack Baldry <jack.baldry@grafana.com>

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

Co-authored-by: Jack Baldry <jack.baldry@grafana.com>

* Update docs/sources/fundamentals/timeseries-dimensions/index.md

Co-authored-by: Jack Baldry <jack.baldry@grafana.com>

* Update docs/sources/fundamentals/dashboards-overview/index.md

Co-authored-by: Jack Baldry <jack.baldry@grafana.com>

* Update docs/sources/fundamentals/dashboards-overview/index.md

Co-authored-by: Jack Baldry <jack.baldry@grafana.com>

* Update docs/sources/panels-visualizations/configure-standard-options/index.md

Co-authored-by: Jack Baldry <jack.baldry@grafana.com>

* Update docs/sources/panels-visualizations/query-transform-data/transform-data/index.md

Co-authored-by: Jack Baldry <jack.baldry@grafana.com>

* Remove grafana.com from 2 URLs

* Fix 1 more reference link

* Prettier fix

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Co-authored-by: Jack Baldry <jack.baldry@grafana.com>

docs/sources/developers/_index.md

@@ -11,7 +11,14 @@ weight: 190
 
 # Developers
 
-This section includes the following Grafana developer documentation:
+Go to the [Grafana developer portal](/developers) to access the following documentation:
+
+- [Grafana plugin development](/developers/plugin-tools)
+- [Grafana design system](https://developers.grafana.com)
+- [Grafana Scenes](/developers/scenes)
+- [Grafana data plane](/developers/dataplane)
+
+This section of our documentation contains additional resources:
 
 {{< section >}}
 
@@ -19,4 +26,3 @@ You might also find the following resources to be helpful:
 
 - [Grafana Tutorials:](https://grafana.com/tutorials/) Step-by-step guides that help you make the most of Grafana.
 - [Grafana Community Forums:](https://community.grafana.com) Get technical support for open source Grafana, Loki, and Tempo.
-- [Grafana design system:](https://developers.grafana.com) Library of reusable Grafana components and guidelines that help you with contribution and plugin development.