Fix parameter naming in AddMongoDB method (#629)

Author: GeertvanHorrik

src/frontend/src/content/docs/integrations/databases/mongodb/mongodb-host.mdx

@@ -86,7 +86,7 @@ var builder = DistributedApplication.CreateBuilder(args);
 var username = builder.AddParameter("username");
 var password = builder.AddParameter("password", secret: true);
 
-var mongo = builder.AddMongoDB("mongo", username, password);
+var mongo = builder.AddMongoDB("mongo", userName: username, password: password);
 var mongodb = mongo.AddDatabase("mongodb");
 
 var myService = builder.AddProject<Projects.ExampleProject>()