Model Request: Blenderbot 2.0

# 🌟 New model addition

## Model description

Facebook released Blenderbot 2.0, a chatbot that builds on RAG and Blenderbot 1.0. It can save interactions for later reference and use web search to find information on the web.

https://parl.ai/projects/blenderbot2/

## Open source status

* [x] the model implementation is available: in Parl.ai
* [x] the model weights are available: https://parl.ai/docs/zoo.html#wizard-of-internet-models
* [ ] who are the authors: (mention them, if possible by @gh-username)