[FEATURE REQUEST] Backup folders for Android device

Is your feature request related to a problem? Please describe.
I'm always frustrated when new photos have been uploaded, but existing photos are ignored.

Describe the solution you'd like
As an user,
I would like to select many folders on my Android device, and I would like ownCloud App to automatically detect if any file does not exist on the cloud and backup them.

For example,
I have a,b,c files on my Android device under folder media, and I choose to backup this folder to ThisBackup folder on ownCloud server, and ThisBackup folder already have a file named Iamhere.mp3 over there.
I added one file d to this folder on my Android device, then, this file is uploaded to owncloud server.
I remove a from this folder, and this a will be removed from owncloud server as well.
There is one exception, Iamhere.mp3 exists before I choose to backup media folder on my Android device to ThisBackup folder, so this file should not be deleted by sync logic.

Describe alternatives you've considered
I can upload mannually, but if I upload one file two times, ownCloud will rename it after upload it, but what I would like it to do is to not upload the file, because it already exists on the owncloud server.

Additional context
No

TASKS

• Research (if needed)
• Create branch feature/feature_name
• Development tasks
  • Implement whatever
  • ...
• Code review and apply changes requested
• Design test plan
• QA
• Merge branch feature/feature_name into master

PR

• App
• Library (if needed)

The issue does not name files, tests, or entry points. Start by reviewing the Android app's existing upload and folder-sync behavior, then clarify how selected folders, existing server files, deletions, and files present before setup should be distinguished. Done means the behavior is specified, implemented, and covered by a test plan for these cases.