Add inputs for scaling benchmarks to examples

[AlexanderSinn]

This PR adds inputs a transverse and a time step scaling benchmark. The transverse benchmark is tested in GPU CI with 1023^2 cells.

• [ ] 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

[AlexanderSinn]

The problem is that most of the runtime is spent computing the fields at  4095*4095*112000. When reducing the resolution by more than 10x the MG solver can stop converging, as the plasma frequency is not resolved properly. I don't think this is possible to run in ~2 min which would be acceptable for a CI test.