Allow for passing additional data to the adapter

[loganek]

As discussed in #14 (comment), we'd like to have a way to pass extra data (e.g. parameters) to the runtime adapter.

We consider 3 options:

1. add --adapter-parameters parameter to a test runner - this was something I wanted to add in the future, just didn't prioritize it yet (I'm happy to accept a PR if that's urgent)
2. use environment variables that can be read by the adapter - this is something that should work even today so you don't need changes in the test runner to have it working
3. dynamically create a file in a specific location (e.g. in adapter's location) and make the adapter read from that location

IMO option 1. provides a consistent mechanism for the adapters and can easily be documented in the CLI interface and consumed by adapters. Nothing stops adapters from using 2. and 3. - if for some reason they need to use the option, they're free to do so (however, it'd be good in that case to understand their usecase and either provide a guidance or improve test runner to support that if it's a generic problem).

Any feedback is welcome.