option to prefer a configured language instead of guessing

implement Pinecone based storage

support GPT4

refactoring to make models selectable

This makes it much easier to add new models. Models can now be selected
via the configuration

allow to restrict access to certain users and groups

add optional conversation logging

This might be useful to debug and monitor the real world usage of the
bot and analyze abuse.

initial checkin. working vector storage and similarity search