[Docs] Add document on "how to create OSD plugin" in the Developer doc site

[manasvinibs]

We have this document in the OSD repo: https://opensearch.org/blog/technical-post/2022/01/dashboards-plugins-intro/ We need this in the developer doc site.

[ashwin-pc]

That article is an introduction to plugins and its lifecycle. "How to create an OSD plugin" is just a tiny paragraph in there and that intentional. Lets move that article as is into the developer docs site, but if we want to keep a dedicated "How to create an OSD plugin" article, lets make it a tutorial for a demo hello world plugin that uses some of the core components from OSD like saved objects, embeddables, expressions and/or data plugin to show how they work together to make a basic plugin.