add tests for producing metadata

common/cpp/include/common/networking.h

producer/api/include/producer/producer.h

producer/api/include/producer/producer_error.h

producer/api/src/producer_impl.cpp

producer/api/src/producer_impl.h

producer/api/src/request_handler_tcp.cpp

producer/api/unittests/test_producer_impl.cpp

producer/api/unittests/test_request_handler_tcp.cpp

tests/automatic/producer/CMakeLists.txt

tests/automatic/producer/beamtime_metadata/CMakeLists.txt

...utomatic/producer/beamtime_metadata/beamtime_metadata.cpp

tests/automatic/producer/beamtime_metadata/check_linux.sh

tests/automatic/producer/beamtime_metadata/check_windows.bat

worker/api/cpp/src/server_data_broker.cpp

worker/api/cpp/src/server_data_broker.h