CI: Add proper testing for distributed dataflows

[phil-opp]

Our current CI test runs the coordinator and two daemons on the same machine. To ensure that dora is able to communicate across machines, we would need to use three different machines with different IPs. I'm not sure if something like this is possible on GitHub actions, so this issue is mostly a reminder to look into this further.

Notes:

• @haixuanTao mentioned the https://github.com/haythem/public-ip in Configurable bind addrs #471 (comment)

[Michael-J-Ward]

As far as I can tell, the examples runners in CI serve as dora's integration tests. Run Completes = Green, but nothing verifies the output of the run - is that correct?

Are any of them deterministic enough that we could throw a snapshot tests on the output / logs - or otherwise test "successful end state"?

[phil-opp]

Yes, we don't very the output, as it's not deterministic enough. We just check the exit code of the process, which should be != 0 when an error occurs. We also have some examples with assertions, for example for verifying that the ROS2 turtle is at a different position at the end of the test (to ensure that it moved).