- This simplifies instrumenting OpenAI calls
- Reuses the literalai OpenAI instrumentation
- Creates a new step for each OpenAI call, with the call details in the generation property

- This makes sure any children step starts after the parent message step
- replaced `generation.settings.model` by `generation.model`

- avoids erroring if a user isn't using `instrument_openai` and hasn't installed openai