Set wait time after charger connect for auto upload

### Actual behaviour
If i connect the power / charger to my phone the app imediatly uploads all the pictures of the day. I connect the power in normal case if the phone is almost empty. Then the upload is starting and uses a lot of power if there are many pictures. Sometimes it is to much power and the phone is shutting down.

### Expected behaviour
Set a timer to wait after I connect the charger. The most users will charge the phone over the night so there is enough time to upload. Older phones are almost unuseable if they are uploading data.

### Steps to reproduce
1. Activate auto upload
2. Enable the feature "on charger only"
3. Got a lot of pictures over the day
4. Connect the phone
5. Have fun if you want to do something else with the phone

### Environment data
Android version: CM13.1

Device model:

Stock or customized system:

Nextcloud app version: 2.0.0

Nextcloud server version: 13.0.3-3