[WIP] Laser Injection

[EyaDammak]

• new beam parameter:
  <plasma name>.can_laser_injection
<plasma name>.injection_product

• new function in PlasmaParticleContainer.cpp: PlasmaToBeam that transfers the plasma ionized electrons in the beam particle container.

• DONE: creation of the function PlasmaToBeam in the PlasmaParticleContainer, function defined in the source code, method defined in hipace.cpp as DoLaserInjection

• TO DO: for loop on the ionised electrons in the plasma particle container to transfer them in an empty beam container and test it.

• 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