[v9.0.x] Docs: Fix broken grafana plugins tutorial links (#52273)

Co-authored-by: Garrett Guillotte <100453168+gguillotte-grafana@users.noreply.github.com>
Co-authored-by: Esteban Beltran <academo@users.noreply.github.com>

docs/sources/developers/plugins/_index.md

@@ -25,8 +25,8 @@ npx @grafana/toolkit plugin:create my-grafana-plugin
 
 If you want a more guided introduction to plugin development, check out our tutorials:
 
-- [Build a panel plugin]({{< ref "/tutorials/build-a-panel-plugin/" >}})
-- [Build a data source plugin]({{< ref "/tutorials/build-a-data-source-plugin/" >}})
+- [Build a panel plugin]({{< ref "build-a-panel-plugin.md" >}})
+- [Build a data source plugin]({{< ref "build-a-data-source-plugin.md" >}})
 
 ## Go further
 
@@ -36,13 +36,13 @@ Learn more about specific areas of plugin development.
 
 If you're looking to build your first plugin, check out these introductory tutorials:
 
-- [Build a panel plugin]({{< ref "/tutorials/build-a-panel-plugin/" >}})
-- [Build a data source plugin]({{< ref "/tutorials/build-a-data-source-plugin/" >}})
-- [Build a data source backend plugin]({{< ref "/tutorials/build-a-data-source-backend-plugin/" >}})
+- [Build a panel plugin]({{< ref "build-a-panel-plugin.md" >}})
+- [Build a data source plugin]({{< ref "build-a-data-source-plugin.md" >}})
+- [Build a data source backend plugin]({{< ref "build-a-data-source-backend-plugin.md" >}})
 
 Ready to learn more? Check out our other tutorials:
 
-- [Build a panel plugin with D3.js]({{< ref "/tutorials/build-a-panel-plugin-with-d3/" >}})
+- [Build a panel plugin with D3.js]({{< ref "build-a-panel-plugin-with-d3.md" >}})
 
 ### Guides