implement arbitrary source, stream and group names

broker/src/asapo_broker/database/encoding.go

broker/src/asapo_broker/database/mongodb.go

broker/src/asapo_broker/database/mongodb_streams.go

broker/src/asapo_broker/database/mongodb_test.go

broker/src/asapo_broker/server/get_commands_test.go

broker/src/asapo_broker/server/process_request.go

broker/src/asapo_broker/server/process_request_test.go

common/cpp/include/asapo/database/database.h

common/cpp/include/asapo/database/db_error.h

common/cpp/include/asapo/http_client/http_client.h

common/cpp/include/asapo/unittests/MockHttpClient.h

common/cpp/src/database/CMakeLists.txt

common/cpp/src/database/encoding.cpp

common/cpp/src/database/encoding.h

common/cpp/src/database/mongodb_client.cpp

common/cpp/src/database/mongodb_client.h

common/cpp/src/http_client/curl_http_client.cpp

common/cpp/src/http_client/curl_http_client.h

common/cpp/unittests/database/test_encoding.cpp

common/go/src/asapo_common/utils/routes.go