Option to selectively include directories with --generate thumbnail flag

[edrock200]

Describe the problem
A clear and concise description of the problem you're looking to solve.

I like the thumbnail feature but it's not great over cloud mounted storage. Would be nice to be able to "grandfather" what is already in place and generate thumbnails for certain paths moving forward without having to break out the content into separate Plex libraries.

Describe any solutions you think might work
Looks like the --generate flag will allow on demand thumbnail generation. If this could be added as an option along with either inclusion or exclusion paths that would be awesome.

Additional context
Thanks in advance for your consideration. I wish I could code. Lol