Run examples in CI

[oberstet]

we now have CI that builds the examples

• https://github.com/crossbario/autobahn-cpp/tree/master/examples
• https://github.com/crossbario/autobahn-cpp/actions

given that, it would be easy to add another CI step in the workflows to:

• start crossbar (as a docker container)
• run all the examples

this upside of such a test: it really is an integration test, because it tests WAMP C++ components against an actually running Crossbar.io WAMP router using actual WAMP sessions - which is exactly what a library user cares about