Always use collection edition for texts #622
Description
Currently, there is still the option to select a collection where to put uploaded files.
The endpoint that actually gets all the available subcollections is a bit of an odd man out and not recreated in REST v2.
It is easier to simply always use edition as the collection for texts (and pages for the planned wdb pages feature).
When uploading TEI files, we should assume edition to be the standard destination.
Other destinations should be inferred from the file path (this is also necessary when uploading non-XML files, e.g. everything that goes into resources/)