Add vectorize RAG example

[ryanking13]

Adds an example using Workers AI + vectorize to create a simple RAG system without any external packages.

1. Convert documents into embedding and store it to vectorize storage
2. Take natural language query, create embedding, query similarity, and retrieve some documents
3. Summarize the result by passing the documents into workers AI prompt.

[hoodmane]

Can it run in CI?

[ryanking13]

Can it run in CI?

This use remote binding so it requires a real account to run (+ it costs). Maybe we can setup a token to run test but not sure if it is really worth it.