Vector search and embeddings generation

[justyns]

For #34

Needs more testing, but so far:

• Added support for generating embeddings using openai, ollama, and gemini
• Stores generated embeddings in silverbullet's native datastore
• Listens for page:index events and indexes pages automatically when they change
• Generates an embedding per paragraph
• Added a new 🤖 virtual page to test searching with

Todo:

• make this whole thing optional
• add docs and make sure to recommend using local first, like ollama
• more testing to make sure nothing blows up