Re-enable GPU CI

[AlexanderSinn]

This PR re-enables the GPU CI now that the desy runners are online again. They now have a different environment and run in a Docker container, hence the need for all the install changes. Currently the runner runs as root inside a directory that needs root access; however, Open MPI does not like to run as root. Because of this, some workarounds are needed:

export OMPI_ALLOW_RUN_AS_ROOT=1
export OMPI_ALLOW_RUN_AS_ROOT_CONFIRM=1

• Small enough (< few 100s of lines), otherwise it should probably be split into smaller PRs
• Tested (describe the tests in the PR description)
• Runs on GPU (basic: the code compiles and run well with the new module)
• Contains an automated test (checksum and/or comparison with theory)
• Documented: all elements (classes and their members, functions, namespaces, etc.) are documented
• Constified (All that can be const is const)
• Code is clean (no unwanted comments, )
• Style and code conventions are respected at the bottom of https://github.com/Hi-PACE/hipace
• Proper label and GitHub project, if applicable