feat(vertexai): Add Live streaming feature

[cynthiajoan]

Description

Add low-latency, two-way interactions with the Gemini 2.0 model, that use text, audio, and video input, with audio and text output.

For Vertex AI in Firebase, Live Model is in Public Preview, which means that the feature is not subject to any SLA or deprecation policy and could change in backwards-incompatible ways.

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