Parallel and Background uploads when sharing files to Cryptomator via the Share function on mobile app

### Please agree to the following

- [X] I have searched [existing issues](https://github.com/cryptomator/android/issues?q=) for duplicates
- [X] I agree to follow this project's [Code of Conduct](https://github.com/cryptomator/android/blob/develop/.github/CODE_OF_CONDUCT.md)

### Summary

Make the share upload progress bar box non blocking on UI, instead a notification can be added for showing upload progress. This would allow for background share uploads to CM as well as allowing user to trigger parallel uploads from the share menu.

### Motivation

Currently when sharing files to encrypt with CM via the share dialog, there's a popup showing status of upload progress. It's a UI blocking popup, and in parallel more files can't be shared to CM. This isn't the best experience, as I can't share multiple files to CM for upload at the same time. Makes the user wait longer to upload their entire directory of files (if files are segregated across different sub folders). If it can be pushed to background, and probably a updating notification can be shown for the upload progress. And this would also allow for invoking multiple share calls to CM in parallel.

### Considered Alternatives

No workaround for the request mentioned above to the best of my knowledge. As the share upload box simply blocks the UI, and even when you share another set of files it shows the progress of the current ongoing upload only. Which has to either complete/be cancelled for new files to be triggered for upload from the share menu.

### Anything else?

_No response_