[WIP] Add Plasma Histogram Diagnostic

[AlexanderSinn]

diagnostic.names = lev0 hist_uz hist_x_ux

hist_uz.base_geometry = histogram
hist_uz.hist_species_names = beam
hist_uz.hist_num_bins = 500
hist_uz.hist_bins_lo = 1980
hist_uz.hist_bins_hi = 2020
hist_uz.hist_function = "uz"

hist_x_ux.base_geometry = histogram
hist_x_ux.hist_species_names = beam
hist_x_ux.hist_num_bins = 500 500
hist_x_ux.hist_bins_lo = -2 -10
hist_x_ux.hist_bins_hi =  2  10
hist_x_ux.hist_function = "x"
hist_x_ux.hist_function2 = "ux"
hist_x_ux.hist_integrate_along_z = true

• 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