add beamline to source credentials (c++), producer retries on reauthorization error

common/cpp/include/common/data_structs.h

common/cpp/include/common/networking.h

common/cpp/src/data_structs/data_structs.cpp

common/cpp/unittests/request/mocking.h

common/cpp/unittests/request/test_request_pool.cpp

producer/api/cpp/include/producer/producer_error.h

producer/api/cpp/src/producer_impl.cpp

producer/api/cpp/src/request_handler_tcp.cpp

producer/api/cpp/unittests/test_producer.cpp

producer/api/cpp/unittests/test_producer_impl.cpp

producer/api/cpp/unittests/test_request_handler_tcp.cpp