copyright checker: fix C/C++ template

[fbaeuerle]

Fix the indentation of the C++ copyright template in order to comply with the Eclipse handbook

[nradakovic]

If we now decide to do it, we will need to update all copyright headers inside all C/C++ files inside project. Is this mandatory change?

[fbaeuerle]

Well, it is not strictly mandatory, but looking at e.g. https://github.com/eclipse-score/baselibs, most of the c++ code uses the formatting that this PR introduces. I suppose in the end we need a formatting that is compatible with clang-format and enforce both the copyright template check and clang-format.