Auto upload - Button to manually scan files in the file system and re-upload missing files.

**Is your feature request related to a problem? Please describe.**
Nextcloud auto upload is buggy and often misses some files. This is an issue that is present since several months / years. See the following discussions:
https://help.nextcloud.com/t/auto-upload-is-skipping-random-pics/222184
https://help.nextcloud.com/t/android-client-does-not-auto-upload-all-images/216849
https://github.com/nextcloud/android/issues/13792
https://github.com/nextcloud/android/issues/14365

There are many more.

**Describe the solution you'd like**
It is observed that if the auto upload is deleted and created again (with the option of uploading existing files) the missing files are uploaded. Since there does not seem an easy fix for this problem, it would be better to surface a button to rescan the file system. That button may internally just delete the auto upload and create it again.

**Describe alternatives you've considered**
Already mentioned above - deleting and recreating the auto upload.

**Additional context**
N/A