Adding DeadRun flag to SIRI for ET and VM

[TuThoThai]

Context

Since we have the possibility to have dead runs in NeTEx, it would be interesting to be able to follow them in SIRI-VM (mostly) and in SIRI-ET. It would allow to address these use cases:

• Have an explicit mention of a dead run that can be used for passenger information, especially when unplanned
• Support fleet monitoring regardless of the ServiceJourney type (accepting passengers or not).

Changes made in this PR

• In the XSD, more precisely in siri_journey.xsd in the JourneyInfoGroup, addition of an optional boolean named DeadRun7 with the default value being false`
• One example of a payload in SIRI-ET that includes a dead run
• One example of a payload in SIRI-VM that includes a dead run

[haeckerbaer]

approved but maybe check the sentence "so it is clear that only there is no expectation of an associated service to it" again.