Add an ImagesLifecycleTask to pass options along to source set tasks

[theisenp]

Context

Right now you can't filter any of the Microfilm tasks. So if you want to compress/verify a specific image, you have to compress/verify the whole module. I think it would be helpful to be able to run tasks on a subset of images, similar to how you can filter tests with the --tests option.

This PR

The new --image option is attached to the source set specific tasks, so this works:

./gradlew compressMicrofilmMain --images="**/my_image.png"

But if you try to pass a filter to the parent task it fails:

./gradlew compressMicrofilm --images="**/my_image.png"

I think this is relatively common for Gradle tasks, but it doesn't feel like a great user experience. I'm proposing that we add an ImagesLifecycleTask that does nothing except pass these options along to the source set tasks. I'm not that familiar with Gradle task options, so if there's a good reason not to do this, let me know!

[eric-labelle]

I'm not that familiar with Gradle task options, so if there's a good reason not to do this, let me know!

also not really familiar with this.
@joshfriend probably has an opinion here :)

[eric-labelle]

approving to unblock the stack, we can revise after if Josh has suggestions/concerns.

[theisenp]

I see that Tony Robalik actually published a blog post yesterday that addresses something similar! It's implemented somewhat differently because, it modifies the existing test task to add this support instead of modifying a custom task owned by a plugin, but conceptually it's similar.

The other takeaway is that "Aggregate" is probably not the right term here (not surprising, I don't know the terminology so I made something up). Tony describes these as "lifecycle" tasks, so I think it makes sense to call this something like ImagesLifecycleTask instead of AggregateTask.

[theisenp]

One thing that we could also do to take this a step further is have CompressTask, DecompressTask, and VerifyTask all extend this base class instead of DefaultTask, so they're all guaranteed to share the same --images option.

Or instead of extending ImagesLifecycleTask directly, we could make something like a HasImagesOption interface that the lifecycle and source set tasks all implement.