Generate docs for function

Author: carlosdelest

docs/reference/query-languages/esql/images/functions/v_cosine.svg

@@ -13,11 +13,13 @@
 import org.elasticsearch.xpack.esql.action.EsqlCapabilities;
 import org.elasticsearch.xpack.esql.core.expression.Expression;
 import org.elasticsearch.xpack.esql.core.tree.Source;
+import org.elasticsearch.xpack.esql.expression.function.FunctionName;
 import org.elasticsearch.xpack.esql.expression.function.TestCaseSupplier;
 
 import java.util.List;
 import java.util.function.Supplier;
 
+@FunctionName("v_cosine")
 public class CosineSimilarityTests extends AbstractVectorSimilarityFunctionTestCase {
 
     public CosineSimilarityTests(@Name("TestCase") Supplier<TestCaseSupplier.TestCase> testCaseSupplier) {