Generating client proxy code using Add WCF Service Reference is missing an endpoint

**Describe the bug**
Generating client proxy code using Visual Studio (Add WCF Service Reference) from service WSDL is missing an endpoint.
Sample code: [WCF Sample MessageEncoder](https://github.com/dotnet/samples/tree/main/framework/wcf/Extensibility/MessageEncoder/Text/CS)

**To Reproduce**
1. Clone the sample code.
2. Enable service metadata behavior in Web.config: ``
3. Build the service (it will be published to IIS) and generate client code using Add Service Reference from service WSDL `http://localhost/servicemodelsamples/service.svc?wsdl`.

**Expected behavior**
The generated client proxy should have two endpoints, default and secure endpoints, but only the default endpoint is generated. The service WSDL looks good, but the generated code is missing secure endpoint.