more work on preoducer

producer/api/CMakeLists.txt

producer/api/src/receiver_discovery_service.cpp

producer/api/src/receiver_discovery_service.h

producer/api/src/receivers_status.cpp

producer/api/src/receivers_status.h

producer/api/src/request.cpp

producer/api/src/request.h

producer/api/src/request_pool.cpp

producer/api/src/request_pool.h

producer/api/unittests/test_receivers_status.cpp

producer/api/unittests/test_request.cpp

producer/api/unittests/test_request_pool.cpp