Support for Extra Call in Siri-ET

[t2gran]

Is your feature request related to a problem? Please describe.

As a ServiceProvider I want to add extra Stop/Quays to a trip on a given date. The stop/quay should already exist in the data.

Goal / high level use-case

When an incident happens, a train or bus may have to change its route and use other stops for part of the trip. We want to allow this as long as the trip visit stops/quays that already exit.

Describe the solution you'd like

We have not looked into what we want to do, but we do generate trip-patterns for GTFS during graph build and for canceled stop today. This is a similar problem.