[FEATURE REQUEST] Recursive batch upscale for nested subfolders

Checklist

• I have checked that this issue isn't addressed in the FAQ.
• I have checked that this issue isn't addressed in any other issue or pull request.

Related Problem(s)

When there is a system file in the folder you are upscaling (Thumbs.db, desktop.ini, .DS_Store, etc.), you will get an error message.

Description

There should be an option when using batch upscale to also upscale all images in subdirectories

Alternatives

You have to manually batch upscale each folder right now, which can be annoying