ktlint check tasks should be cacheable

[eskatos]

The ktlint check tasks created by this plugin don't have any output registered, so they are never up to date and cannot be cached by the Gradle build cache.

The report files generated by those tasks should be registered as outputs and the task marked as cacheable.

Other tasks contributed by this plugin might be good candidates for build cache too, I just didn't look at them closely.

[JLLeitschuh]

This is generally a hard problem given the API that Gradle exposes.
See the forum post by @nedtwigg about it in Spotless:
https://discuss.gradle.org/t/two-cases-where-the-incremental-api-is-lacking/24266

[Tapchicoma]

I think there is no reason to make ktlintFormat type tasks cacheable, but definitely worth for ktlintCheck tasks!

[wolfs]

The check task is now cacheable since #90 has been merged.

[JLLeitschuh]

@wolfs Thank you for the great work!

[Tapchicoma]

Closing this as @wolfs implemented it.