Make various AI embeddings settings and chat options configurable.

The short version is this implements all of the @todo comments about making options configurable as well as the @todo about making ChatForm backend-agnostic.

1. Make various AI embeddings settings and chat options configurable with a debug option to show them on the front-end.
2. Implement search() in the Pinecone backend so that the Search API query can be executed directly in ChatForm (and therefore ChatForm becomes generic and does not need a reference to the Pinecone backend).
3. Add a debug option to the ChatFormBlock that shows the current settings on the front-end for easier debugging/demoing.

Configuration options (other than index because this is essential) are passed to the ChatForm in build info with the key chat_config. ChatForm also has its own defaults for each chat_config setting so that the settings are optional.

Debug info screenshot:

Config form screenshot: