Support for `--folder` and `--user` parameters in `occ recognize:classify`

Describe the feature you'd like to request

I use nextcloud together with memories to browse my pictures. It integrates Recognize as part of its features to tag the content of the pictures themselves.

I have a collection of hundreds of thousands of pictures on network drives, which are accessed via nextcloud's external storage. Moreover, I have several test users that have access to those files, but don't use them actively, so the whole picture library is actually duplicated several times in nextcloud database.

So, when running a full indexing of my library, something I'm aware it can take several days, I'd like to skip those users and folders that I know don't contain any pictures or won't be used at all.

Describe the solution you'd like

I would love if there was some parameter in the occ recognize:classify to specify for which user I'd like to run the classificator, or limit it to a specific folder subtree. For instance:

occ recognize:classify --user myuser --folder "Media/Pictures"

This would limit the classification to my user, and circumscribed to my picture folder only (I don't need recognize to scan all my documents or work files). And would save me several days of processing time.

Describe alternatives you've considered

The only alternative would be to set up a separate nextcloud installation with only that user and an external storage pointing to the specific path of the picture library. But it's not realistic.

Start at the occ recognize:classify command entry point and trace how users and folders are currently selected for classification. Define how --user and --folder should combine, then verify that the example command limits processing to the requested user and folder subtree without affecting unrestricted classification.