chore: add property frequencyPenalty in type defintions

[bearjaws]

Hey all, was working with gemini-flash-1.5 and noticed that frequencyPenalty was not documented in typescript. Taken from these docs: https://cloud.google.com/vertex-ai/generative-ai/docs/model-reference/inference

I validated that it gets parsed into formulateRequest in generative_models.js when calling generateContent.

One item I was not sure about was how much input validate we want to add?

I see we are validating topK in validateGenerationConfig but that is the only thing, all other properties are missing and will error out on the API side.

Let me know if you want me to add checks there or change anything else. I have signed the Contributor License Agreement

Thank you!