[Feature Request] Add an option to merge documents

[wallace11]

Hi there,
Sometimes you'd want to keep multiple documents under the same item ("All files are one single item") after they're uploaded (i.e. during documents organization after an email import or scanning lots of documents).
The only way to do that now is to remove existing items and then reupload them to an existing item.
Instead, I suggest having an option to do that on already uploaded documents :)

Thanks.

[eikek]

I have good news then - this is already implemented :) just not released yet. But you can test it out on the nightly version of Docspell.When doing this, I would recommend to copy the database, because nightly versions may have bugs. See #414 for reference.

[wallace11]

Hey, NICE!
I've actually got Docspell set up with the nightly version on a different Docker stack than my "production" version, but never noticed this change.
Thank you so much for your hard work!