[Android] Share support for Nextcloud Bookmarks

### Describe the feature you'd like to request

Nice to have. Share support when available from Nextcloud Bookmarks.

### Describe the solution you'd like

- Could be added to (...) menu
- Accessible when editing a bookmark or folder.
- Retrieve shared url
- Retrieve RSS feed
- Visual indication when a bookmark is shared.
- Create a share directly from the Floccus Android app.

### Describe alternatives you've considered

Browse to Nextcloud Bookmarks webui