Add opportunity to use selection

[InsanusMokrassar]

It would be nice to have opportunity to use selection from variants instead of raw strings. For example, we have several variants of plugin: jvm, multiplatform, js. So, we could set it as array in config:

{
    ...,
    "sample_selection": ["jvm", "multiplatform", "js"]
    ...
}

And for variable sample_selection to have opportunity to choose one of variants in plugin window in IDEA