We are clearly not using these containers anymore, as they fail to build:
0.297 Err:4 http://deb.debian.org/debian buster Release 0.297 404 Not Found [IP: 199.232.190.132 80] 0.305 Err:5 http://deb.debian.org/debian-security buster/updates Release 0.305 404 Not Found [IP: 199.232.190.132 80] 0.314 Err:6 http://deb.debian.org/debian buster-updates Release 0.314 404 Not Found [IP: 199.232.190.132 80] 0.320 Reading package lists... 0.334 E: The repository 'http://deb.debian.org/debian buster Release' does not have a Release file. 0.334 E: The repository 'http://deb.debian.org/debian-security buster/updates Release' does not have a Release file. 0.334 E: The repository 'http://deb.debian.org/debian buster-updates Release' does not have a Release file.
This container does not build anymore (fails on "License classifiers have been superseded by license expressions" while installing lcov-to-cobertura-xml with pip). This means it is unused, remove it.
This container is not being used, and it still attempts to install python2 which has been removed from debian sid quite some time ago. Let's remove it.
We aren't using gravatar or other 3rd party avatar services, and we don't want the default avatars either as they can give the same color to different users, making them look like the same user on first glance.
* Use the redmine:6.1.3 image from upstream (the sysmocom registry image was a workaround for 5.1.11).
* Install nkf with native extensions (needs gcc, libc6-dev, make) for the redmine_openid_provider plugin. This was not needed for the redmine 5 container, it was probably bundled there already.
* Upgrade "activerecord-session_store" to version 2.2.0, which is compatible with redmine 6.
