add option to not deposit Jx and Jy of the beam

[SeverinDiederichs]

This PR adds the possibility to neglect Jx and Jy of the beam, via the parameter
hipace.do_beam_jx_jy_deposition = 0 (default is 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

[MaxThevenet]

@jlvay @RemiLehe @ax3l:
@SeverinDiederichs identified the source of this noise: it appears when we deposit the transverse currents of the beam, and when there are not that many beam particles. Hipace doesn't deposit the transverse current, so this PR implement the option to do the same.

[ax3l]

Awesome, glad you found the source of this!