Add KOTLIN_SCRIPTS feature flag

[jmfayard]

Minimum viable PR for #582

Discussion should happen in the issue

[jmfayard]

@LouisCAD I commented on your idea to have something independant from Gradle here https://github.com/jmfayard/refreshVersions/issues/586

I still think there is no issue with adding Kotlin Script support in the current codebase. Because there is no issue with refactoring later the "Add KTS support" part of the codebase with the rest of the codebase.

Something I need to clarify is that I do not want to implement Kotlin Scripts support in one large pull request here like I did for Gradle Versions Catalogs.

I learned my lesson that small is beautiful, and having multiple small pulll requests is less work and less stress for everyone that one huge pull request that does everything. So this particular PR has the narrow goal of adding the feature flag and having a high level discussion on how the feature should look like but nothing more. That's why incidently there is no real point of adding feature flags support in RefreshVersionsCleanupTask.kt in a separate PR. Adding the feature flag is my main focus here.

[LouisCAD]

I don't think that getting this PR merged or not is an actual blocker to start working/iterating on the kotlin scripts support feature, but since we might want to add further feature flags at some point, which would generate little git conflicts, I guess it's a good idea to merge it now.