Add Model Armor config support to Python Gen-AI library

[tanmha]

The Vertex AI REST API defines a ModelArmorConfig object with promptTemplateName and responseTemplateName fields to apply Model Armor templates during inference.

Please expose an equivalent ModelArmorConfig class in the Python Gen-AI SDK and allow it as an optional argument in model invocation calls.

[janasangeetha]

Hey @tanmha
Thank you for your feedback. We appreciate you taking the time to share your thoughts with us, and we'll be filing a feature request.