[Docs] Reflect the current mapping logic of reasoning effort for Gemini in Vertex AI

[apstndb]

The current documentation only describes the reasoning_effort → thinking budget mappings for Gemini models on Vertex AI (Agent Platform):

litellm-docs/docs/providers/vertex.md

Lines 842 to 855 in 6e7d600

	### **Thinking / `reasoning_content`**
	LiteLLM translates OpenAI's `reasoning_effort` to Gemini's `thinking` parameter. [Code](https://github.com/BerriAI/litellm/blob/620664921902d7a9bfb29897a7b27c1a7ef4ddfb/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py#L362)
	Added an additional non-OpenAI standard "disable" value for non-reasoning Gemini requests.
	**Mapping**
	| reasoning_effort | thinking |
	| ---------------- | -------- |
	| "disable" | "budget_tokens": 0 |
	| "low" | "budget_tokens": 1024 |
	| "medium" | "budget_tokens": 2048 |
	| "high" | "budget_tokens": 4096 |

However, LiteLLM currently also has reasoning_effort → thinking level mappings for Gemini 3.x models in the implementation:
https://github.com/BerriAI/litellm/blob/72fdccb9371cf07d6a90b8a7cde99cd06be1fc1d/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py#L1150-L1177

Could you update the documentation to include the reasoning_effort → thinking level mappings for Gemini 3.x models as well? That would make the docs more consistent with the current implementation.