The configuration did not allow the update of applications which were
shipped with nextcloud. While the updates are downloaded and put into
the custom_apps folder, Nextcloud will continue to use the old app
because it loads it from the first app folder it finds it in.
The `*/*/Dockerfile` are created from `Docker*template` by the
update.sh script. We add a comment at the beginning of the file with
information to find their origin. We also make them readonly to remind
people who would like to improve these files that they are not meant
to be modified.