Allow passing arbitrary arguments to ChatVertexAI and ChatGoogleGenerativeAI

[hassiebp]

Hi team!

Context
ChatOpenAI and ChatAnthropicAI allow passing additional model arguments beyond the available options to their constructors. These additional params will then be passed as an additional config in the LLM call.

• ChatOpenAI has configurable
• ChatAnthropic has invocationKwargs

Idea
It would be great to have the same options for ChatGoogleGenerativeAI and ChatVertexAI . This will allow library users to dynamically set model parameters, and to quickly add newly supported parameters by LLM providers without waiting for SDK upgrades.