Openpmd-api: No verbose output whether openPMD-api was found or not via CMake

[PrometheusPi]

When including openPMD-api in a project compiled using CMake, the fact whether openPMD-api was found or not during linking/compiling is not communicated verbosely.

This could be solved by the host code adding CMake messages manually as done in this pull request, but it would be more convenient if openPMD-api could provide such output on its own as e.g. ADIOS does.

[ax3l]

We use ADIOS1 in PIConGPU with a self-written, old find-module that does such verbose output.

With modern CMake packages and especially the config-module that is being used, It is indeed the right thing to add the extra output depending on the openPMD_FOUND variable as you did these days.

[PrometheusPi]

@ax3l Thanks for your feedback. With the information that the user need to implement the output, the issue can be closed, do you agree?

[ax3l]

Thanks, yes I agree. Thank you for raising the question!