feat(gemini) Update documentation with new property

Author: terussell85

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

@@ -84,6 +84,7 @@ The prefix `spring.ai.vertex.ai.gemini.chat` is the property prefix that lets yo
 | spring.ai.vertex.ai.gemini.chat.options.presencePenalty |  | -
 | spring.ai.vertex.ai.gemini.chat.options.functions | List of functions, identified by their names, to enable for function calling in a single prompt requests. Functions with those names must exist in the functionCallbacks registry. | -
 | spring.ai.vertex.ai.gemini.chat.options.proxy-tool-calls | If true, the Spring AI will not handle the function calls internally, but will proxy them to the client. Then is the client's responsibility to handle the function calls, dispatch them to the appropriate function, and return the results. If false (the default), the Spring AI will handle the function calls internally. Applicable only for chat models with function calling support | false
+| spring.ai.vertex.ai.gemini.chat.options.safetySettings | List of safety settings to control safety filters, as defined by https://cloud.google.com/vertex-ai/generative-ai/docs/multimodal/configure-safety-filters[Vertex AI Safety Filters]. Each safety setting can have a method, threshold, and category. | -
 
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