Exposing output file for reporters in plugin ktlint properties

[Verichev]

We would like to have the option to choose the location for reporter, which in ktlint is optional, but in plugin it's hardcoded and not available for setting.

        project.layout.buildDirectory.file(project.provider {
            "reports/ktlint/${[email protected]}.$fileExtension"
        })

[JLLeitschuh]

PRs are more than welcome to add this feature.