Fix tmpdirs not being removed in Dolos API

[rien]

We've had some issues with the /tmp directory filling up with the result files that were not removed at the end of an analysis, ultimately filling up the storage space (and causing Dolos to give 500 errors).

This was caused by dolos running as root in the container. The files that were created during the analysis could therefore not be removed by the webserver because it did not have the correct permissions. The error was hidden by another bug where the argument verbose: true to the method remove_entry_safe, which was actually interpreted as force = true which ignores errors.

This PR changes the default user of the Dolos docker container to node and sets the container uid to that matching the current user running the webserver. The resulting files should be owned by the current user and should be removed again.

I have pushed this change with ghcr.io/dodona-edu/dolos:2.5.1-1 to let the CI succeed.