Add Sui Framework docs to Reference node

[randall-Mysten]

Add the Sui Framework docs generated from https://github.com/MystenLabs/sui/pull/4993 to the docs site.

1. Create a reference folder in /docs/src
2. Create navconfig.json for the framework docs
3. Move existing Reference topic under Build to the new Reference node
4. Create a Reference landing index page to introduce the References in the node.
5. Add the Event Types docs to the reference node as well (https://docs.sui.io/devnet/build/pubsub#events)

[randall-Mysten]

Added reference node and index topic for this, it currently points to the folder in the repo until Eng can implement adding the files to the site.