This PR introduces the baseline `@webstudio-is/ai` package which
includes:
1. A LLM Abstraction (types) for messages format to make requests to a
model
2. An implementation of the above that uses the OpenAI chat completion
endpoint
3. A common interface for chains. Chains are regular async functions
that can execute an arbitrary number of steps, including calling a LLM
via a model client.
The idea is that a builder API route can use any of these chains to
perform a task that requires AI. For example generate text copy, images,
a theme etc.
