Export CMake Targets and make relocatable

[pascalauroboa]

When building pal_statistics using yocto the generated *Config.cmake files contain absolute paths on the host machine which should not be present when the files are installed onto a target device. This PR makes the exports relocatable and adds modern cmake targets which downstream projects can use like this:

find_package(pal_statistics REQUIRED)

add_library(mylib SHARED ...)

target_link_libraries(mylib PUBLIC pal_statistics::pal_statistics)