openPMD: read input beam from HDF5 file

[AlexanderSinn]

Small tweaks: manly to use make_constants_SI() function instead of hard-coded variables.

This PR implements functionality to use a HDF5 file as a beam input.
To compile use:

-DHiPACE_OPENPMD=ON

Use the file (e.g. beam_00000.h5 ) with

beam.injection_type = from_file \
beam.input_file = beam_%T.h5 \

The Beam has to be in iteration 0 of the file. The physical quantities (r ,u ,q, m) can be named arbitrarily, however the corresponding units have to be correct. The coordinate Axis are assumed to be named x y z or X Y Z.
If not it is possible to specify new names with

beam.file_coordinates_xyz = x1 x2 x3 \

to map file coordinates x1 x2 x3 to Hipace coordinates x y z. This can also be used to swap coordinates (e.g. x and z)

beam.file_coordinates_xyz = z y x \ 

Since Beam Particle mass is currently not used it is optional in the file, but if specified the ratio Charge / Mass has to match that of Electrons.

In /tools the python script write_beam.py can be used to write a beam file which matches the Beam created by a fixed_weight Blowout wake from the examples.

If normalized Units are used then the plasma density must be specified:

beam.plasma_density = 2.8239587008591567e23 \

• 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]

Looks good to me, thanks! Just one formatting point: for the preprocessor directives, could you remove the indentation for all of them (I wrote a suggestion just for one of them)? Just to be consistent with the rest of the code.
git grep " #" will show you where these directives are indented.

[MaxThevenet]

Suggested change

	#ifdef HIPACE_USE_OPENPMD
	#ifdef HIPACE_USE_OPENPMD

[MaxThevenet]

Thanks for this PR!