Add googleSearchRetrieval as an option for VertexAIGeminiChatOptions

- Add test

spring-ai-docs/src/main/antora/modules/ROOT/pages/api/chat/vertexai-gemini-chat.adoc

@@ -68,6 +68,7 @@ The prefix `spring.ai.vertex.ai.gemini.chat` is the property prefix that lets yo
 
 | spring.ai.vertex.ai.gemini.chat.options.model | Supported https://cloud.google.com/vertex-ai/docs/generative-ai/model-reference/gemini[Vertex AI Gemini Chat model] to use include the (1.0 ) `gemini-pro`, `gemini-pro-vision` (deprecated) and the new `gemini-1.5-pro-001`, `gemini-1.5-flash-001` models. | gemini-1.5-pro-001
 | spring.ai.vertex.ai.gemini.chat.options.responseMimeType | Output response mimetype of the generated candidate text. |  `text/plain`: (default) Text output or `application/json`: JSON response.
+| spring.ai.vertex.ai.gemini.chat.options.googleSearchRetrieval | Use Google search Grounding feature | `true` or `false`, default `false`.
 | spring.ai.vertex.ai.gemini.chat.options.temperature | Controls the randomness of the output. Values can range over [0.0,1.0], inclusive. A value closer to 1.0 will produce responses that are more varied, while a value closer to 0.0 will typically result in less surprising responses from the generative. This value specifies default to be used by the backend while making the call to the generative. | 0.8
 | spring.ai.vertex.ai.gemini.chat.options.topK | The maximum number of tokens to consider when sampling. The generative uses combined Top-k and nucleus sampling. Top-k sampling considers the set of topK most probable tokens. | -
 | spring.ai.vertex.ai.gemini.chat.options.topP | The maximum cumulative probability of tokens to consider when sampling. The generative uses combined Top-k and nucleus sampling. Nucleus sampling considers the smallest set of tokens whose probability sum is at least topP.  | -