Allow Export As dialog to write exported file directly to a Nextcloud folder

[sebastiaanveld]

Is your feature request related to a problem? Please describe.
When a user has a file opened in Draw.io and click File> Export As, the workflow allows only to select the Local Device as a Save As/Download Target. It would be helpfull id the exported file could be saved directly to a Nextcloud Folder.

• Open an .drawio file in Nextcloud
• Click File> Export As
• Select PNG (as an example)
• Click Export in the dialog
• The Save As dialog that appears only shows the "Device" as a target and a "Download" button

• The file will be save locally on the device
• User needs to close Draw.io and upload the exported PNG file back to Nextcloud

Describe the solution you'd like
Nextcloud Office/Collabora Office allows while editing a document from Nextcloud to be Exported directly to a Nextcloud Folder. This is usefull as it won't save files locally. For this they "split" the dialogs into "Export As" and "Download As" where Export As saves the file directly to the Nextcloud folder. Download As obviously download the file to the local device.

For Draw.io Nextcloud App It would be nice to have the Export As/Save As dialog allow the selection of the Nextcloud instance to save the file to, like in this example (the Download button may be changed to "Save" in this case):

Describe alternatives you've considered
Alternative the user needs to save files locally first and then upload those back into a Nextcloud Folder.

Additional context
Reason why it's nice to export files directly back to Nextcloud is:

• No need to save files locally (which gets messy when lots of files are changed for documentation purposes) and uploading to nextcloud
• Creating document in Nextcloud with Office allows pictures that you want to insert into you document be taken directly from a Nextcloud folder. So if files Exported from Draw.io could be saved directly into those folders that would be time saving and be a consistent workflow for users where all data stays within Nextcloud.

The Insert "Image dialog" in Nextcloud Office allows selecting a file directly from a Nextcloud Folder.