Add support for offline mode for Document Provider

### ⚠️ Before posting ⚠️

- [X] This is a **bug**, not a question or an enhancement.
- [X] I've [searched for similar issues](https://github.com/nextcloud/android/issues) and didn't find a duplicate.
- [X] I've written a clear and descriptive title for this issue, not just "Bug" or "Crash".
- [X] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/).

### Steps to reproduce

1. Go Offline
2. Take any app that can export files
3. In the "Save As" Dialog, select a Nextcloud Folder
4. "Document could not be saved"

### Expected behaviour

1. Go Offline
2. Take any app that can export files
3. In the "Save As" Dialog, select a Nextcloud Folder
4. File is saved localy
5. As soon as you go online, the file will be uploaded

### Actual behaviour

I want to use this feature, for an app that creates an backup every day, scheduled.
It would be super handy if one could just use this procedure.

If you are online it works fine
But if you are offline, the export fails and even creates an error within that app. In a backup scenario, this is a serious error

Also, the file picker offers those Folders. So Nextcloud should not cause errors to other apps, when you chose Nextcloud Folders.


### Android version

LinageOS 20

### Device brand and model

Google Pixel...

### Stock or custom OS?

Custom (explain in "additional information")

### Nextcloud android app version

3.27.0

### Nextcloud server version

27.1.5

### Using a reverse proxy?

No

### Android logs

_No response_

### Server error logs

_No response_

### Additional information

_No response_