Install sdk_info.h even if RERUN_INSTALL_RERUN_C option is OFF

[traversaro]

What

Since rerun 0.18, the C++ public headers now include the rerun/c/sdk_info.h header, so the rerun/c/sdk_info.h file needs to be installed even if the C static library is not installed, i.e. if RERUN_INSTALL_RERUN_C CMake option is set to OFF.

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[Wumpf]

great catch, completely missed that this could be an issue when adding sdk_info.h