metricq-cpp FTBFS with protobuf >=22

[cvonelm]

metricq-cpp fails to build with protobuf versions >= 22 due to two issues:

1. protobuf 22 added Abseil as a dependency, but FindProtobuf.cmake does not take care of this dependency. This can be fixed by adding Abseil as a dependency to the metricq-protobuf target if versions >= 22 are detected.
2. Additionally there seem to be breaking changes to the API:

[ 43%] Building CXX object CMakeFiles/metricq-source.dir/src/source.cpp.o
In file included from /include/google/protobuf/implicit_weak_message.h:39,
                 from include/google/protobuf/generated_message_util.h:55,
                 from include/metricq/datachunk.pb.h:27,
                 from metricq-cpp/src/source.cpp:33:
include/google/protobuf/repeated_field.h: In instantiation of 'class google::protobuf::RepeatedField<const long int>':
include/metricq/types.hpp:131:71:   required from here
include/google/protobuf/repeated_field.h:155:42: error: static assertion failed: We do not support const value types.
  155 |   static_assert(!std::is_const<Element>::value,
      |                                          ^~~~~
include/google/protobuf/repeated_field.h:155:42: note: '!(bool)std::integral_constant<bool, true>::value' evaluates to false
include/google/protobuf/repeated_field.h: In instantiation of 'class google::protobuf::RepeatedField<const double>':
include/metricq/types.hpp:132:54:   required from here
include/google/protobuf/repeated_field.h:155:42: error: static assertion failed: We do not support const value types.
include/google/protobuf/repeated_field.h:155:42: note: '!(bool)std::integral_constant<bool, true>::value' evaluates to false
make[2]: *** [CMakeFiles/metricq-source.dir/build.make:76: CMakeFiles/metricq-source.dir/src/source.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:453: CMakeFiles/metricq-source.dir/all] Error 2
make: *** [Makefile:166: all] Error 2

[bmario]

CMake Issue: https://gitlab.kitware.com/cmake/cmake/-/issues/25079