Install appropriate version of TestNg in user project depending on JDK version

[EgorkaKulikov]

Description

If JDK version is 11 or higher, we can still install release version of TestNg
Otherwise we should install 7.5 version as higher versions of this framework require JDK 11
https://groups.google.com/g/testng-users/c/BAFB1vk-kok

Context

This issue can be implemented after the increasing of intellij-gradle-plugin version from 2020.2

[tyuldashev]

Additional current problem is that even if user already have properly installed Java 1.8 + TestNG 7.5 she still cannot select TestNG as test framework for test generation.