Update Vertex AI embedding to allow a batch size of 250 (langchain4j#556

)

langchain4j-vertex-ai/src/main/java/dev/langchain4j/model/vertexai/VertexAiEmbeddingModel.java

@@ -46,7 +46,7 @@
  */
 public class VertexAiEmbeddingModel implements EmbeddingModel {
 
-    private static final int BATCH_SIZE = 5; // Vertex AI has a limit of up to 5 input texts per request
+    private static final int BATCH_SIZE = 250; // Vertex AI has a limit of up to 250 input texts per request
 
     private final PredictionServiceSettings settings;
     private final EndpointName endpointName;