fix: CMake/protobuf/abseil, fixes #38

This uses the config version of FindPackage.
But we have to sue the module compatibiltiy, because the build commands of config version are totally different and undocumented.

see protocolbuffers/protobuf#12637 (comment)
see https://stackoverflow.com/a/56896032/620382

CMakeLists.txt

@@ -8,7 +8,9 @@ include(cmake/DefaultBuildType.cmake)
 include(cmake/GitSubmoduleUpdate.cmake)
 git_submodule_update()
 
-find_package(Protobuf 3.0 REQUIRED)
+set(protobuf_MODULE_COMPATIBLE ON CACHE BOOL "")
+find_package(Protobuf CONFIG REQUIRED)
+
 find_package(Git)
 
 if(NOT METRICQ_POSITION_INDEPENDENT_CODE)