Update Google Cloud Generative Model Hooks/Operators to bring parity with Vertex AI API

[CYarros10]

With the constantly evolving Vertex AI APIs for generative models, this PR updates the generative_model hooks/operators in the following ways:

• naming conventions in line with Vertex AI APIs
• consolidation of multimodal operators into a single GenerativeModelGenerateContentOperator
• addition of contents and tools parameters for greater flexibility interacting with Vertex AI APIs
• docs updates
• provider dependency upgrade for aiplatform package

for more information visit: https://cloud.google.com/vertex-ai/generative-ai/docs/start/quickstarts/quickstart-multimodal

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[CYarros10]

@shahar1 Thank you for your feedback. I agree with your points. I'll add a commit that retains the old operators/hooks and include deprecation warnings.

[potiuk]

conflicts