add plugin framework docs

Author: joshuali925

DEVELOPER_GUIDE.md

@@ -243,6 +243,7 @@ Now that you have a development environment to play with, there are a number of
 
 - [Introduction to OpenSearch Dashboards Plugins](https://opensearch.org/blog/dashboards-plugins-intro/) blog post
 - [OpenSearch Dashboards plugin user documentation](https://opensearch.org/docs/latest/install-and-configure/install-dashboards/plugins/) (install, update, and remove)
+- [Plugin framework guide](docs/plugins/plugin-framework-guide.md)
 - Much of the technical architectural information about the plugin system is located in `/src/core`
   - [README](https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/core/README.md)
   - [Plugin principles](https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/core/PRINCIPLES.md)

docs/_sidebar.md

@@ -22,6 +22,7 @@
     - explore
       - [Query panel actions](plugins/explore/query-panel-actions.md)
     - [Data_persistence](plugins/data_persistence.md)
+    - [Plugin framework guide](plugins/plugin-framework-guide.md)
   - Saved_objects
     - [Saved_object_repository_factory_design](saved_objects/saved_object_repository_factory_design.md)
   - Telemetry