An API key (StoredKey or string) or a function returning the API key for OpenAI.
Defaults to StoredKey("OpenAI") unless baseURL is set to a different value.
It is strongly recommended to use StoredKey for passing and storing secret keys. For example, you can create a key “AnotherOpenAIKey” and set the apiKey parameter to StoredKey("AnotherOpenAIKey").
apiKey