Add analyze methods for getting metadata

[p8]

Besides processing images it would be nice to analyze images as well to get metadata like: width, height and rotation.
This is currently based on the ActiveStorage::Analyzer::ImageAnalyzer. I'd like to move that logic to ImageProcessing instead.

ActiveStorage currently logs if analyzing doesn't work, or if the image is invalid. Not sure if we should raise an error in analyze instead, or maybe keep the image validation out of analyze.

[p8]

It would be nice to add fastimage as an analyzer as well.

[sandstrom]

See this thread for an earlier discussion on this topic: #41

I think Janko prefers to keep the scope of this gem down (focused in processing), and I think his argument would also be that it's only a few lines of code, and doesn't really need a separate library. For example, here is the rails analyzer using vips:

https://github.com/rails/rails/blob/684e7609a7a9341fdc6d55956d0b61f58a701e96/activestorage/lib/active_storage/analyzer/image_analyzer/vips.rb