fix(ui): disable save button until the upload file is uploaded / ready

[PatrikKozak]

What?

Previously, while uploading a file - if the uploading process took a bit of time, users could still save the document prior to the upload fully completing.

Why?

During the uploading process - the save button should be disabled until the upload is complete to prevent premature saving of an upload document.

How?

Now, we keep track of the state of the upload in a provider and disable the save button until the file is fully uploaded.

[DanRibbens]

Is there a reason we wouldn't want to add the upload status to the existing DocumentInfoProvider? I don't see what we gain by adding another provider.