feat(artillery): add ability to specify scenario to run by name

[bernardobridge]

Why

Originally requested here #1929, this is a useful feature for people who are saving multiple scenarios in the same file. Especially useful once you start having complex scenarios with weights, but still want the ability to run them individually on demand, a requirement I've had myself in the past.

Note: CLI flag name (--name) could be changed to something else, like --byName. Please suggest something else if you think it makes more sense.
Note: Flag name is now --scenario-name after some internal discussions. Please make other suggestions if other ideas pop up.

[bernardobridge]

@hassy made the changes we discussed (expose to Lambda, and error instead of logging).

I went with erroring from within here a5604ae (i.e. worker level), rather than earlier in the script. The reason is that this way it's not dependant on run command implementation, which means it should work with Fargate (which doesn't have access to the test object from within the command, so has to do these validations at worker level anyway). This is also where the logic of weight picking is, so it felt natural to have that there for now. We can revisit that later IMO, but let me know if you think it shouldn't be here.

Screenshots of errors:

Scenario Not Found

Multiple Scenarios Found

[bernardobridge]

I've made this work with Lambda now, and tested it 👍. Both happy path and errors work now.

Fargate support will require updating platform-fargate, which I'll do next.