Auto Upload detecting deleted pictures

### Is your feature request related to a problem? Please describe.
I was using Google Photos for the last few years. Now, coming to Nextcloud, I miss the chance to sort photos out after they have been taken. Photos are immediately uploaded but usually I review them a few hours later. Only the best photos should remain in the cloud. Bad photos locally deleted should also be deleted online.

### Describe the solution you'd like
Photos taken are automatically upload but when I delete some of them a few hours later, they are deleted in the cloud as well. I wan't to review the locally stored photos so that I can check them even without Internet connection.

### Describe alternatives you've considered
It is possible to browse the photos within the NextCloud App (via Photos). This, however, requires a stable and fast internet connection. This is not sufficient for me.

### Additional context
Keep in mind that it still has to be possible to delete old photos locally from the phone to free up space. In this case, of course, all photos have to stay in the cloud.

Google solves that by providing an app for managing photos on the phone. Pictures can be view locally and deleted in this app. Deleted pictures are also deleted on Google Photos online. In addition, there is a function called "Free phone space" which suggests to delete all photos already uploaded.

Feature was also discussed in the forum: https://help.nextcloud.com/t/how-does-sync-in-mobile-app-works-with-removing-files/22959/6