Improved plugin documentation
https://docs.google.com/document/d/1zjR1FFh_GeVoyRLQUIJkKJxZa4mfVo0yS_ArauwfrGk/edit?usp=sharing
- More logical sorting for the plugins (alphabetical)
- Rename “Get started with plugins” -> Introduction to plugins
- Move “Plugin entry points” into “Explanation”
- Delete “contains” from the third sentence in the plugin introduction page
- Changed the ordering of pydantic model fields: non-optional fields are shown first