NEXUS-7608: Rubygems trials

"Trials" are meant to be executed manually, to "sanity check" but also exercise some  feature of NX, and they usually require some external tooling too (as usage is being simulated with tools that feature is for, like npm CLI, gem/ruby tools, etc). 

Currently "trials" are under modern ITs module and have suffix of `Trial`, hence, are compiled but not executed as part of ITs. This is only PoC to have Trials run leveraging modern IT infrastructure, but Trial Scenarios could be run in many other ways too (are decoupled from ITs), like using some "manually" prepared NX instance and executed via groovy scripting or so (TBD). Scenario is "one unit" of work, that might be even executed in parallel, to form a "load test" basis, but, unlike we do in ITs, the load would be produced using "native/real tools" instead of recorded traffic or such.

Requires:
* bash on path (shell command execution)
* rvm on path (ruby env)
* git on path (hola scenario)

To execute the trials you'd do:
* verify requirements are fulfilled
* execute `mvn -f testsuite/modern-testsuite/pom.xml clean verify -Dtrial`

w/o `as List` I get warnings in IDE... and I hate warnings, as one needs to run the IT to check will they result in RT Ex or not... that's all. 

It might be IDEA groovy support bug, as after removing `as List<String>` from sources did not make IT broken, they passed locally OK.