Versioned docs

[KyleFin]

Describe what scenario you think is uncovered by the existing examples/articles
riverpod.dev/docs continues to evolve with the framework. Thank you! However, this can make it difficult to reference prior versions of the docs. For example, v2.0 docs had:

• explanation of the various provider classes
• syntax for defining notifiers (including family and autoDispose variants)
• a sample createContainer test helper function (https://riverpod.dev/docs/whats_new#providercontainertest)

Each of these has changed in v3.0 and I'm struggling to find the old documentation to explain best practices to teammates while we prepare for an eventual migration to v3.0

Additional context
I think it would be great if the docs could be versioned similar to pub.dev and API reference

[liitx]

This is a great idea--helps with visibility--TY!