Update protobuf repo/fix breaking changes

CMakeLists.txt

FEATURES.md

conanfile.py

include/caosdb/connection.h

include/caosdb/data_type.h

include/caosdb/entity.h

include/caosdb/file_transmission/download_request_handler.h

...e/caosdb/file_transmission/register_file_upload_handler.h

include/caosdb/file_transmission/upload_request_handler.h

include/caosdb/info.h

include/caosdb/message_code.h

include/caosdb/transaction.h

include/caosdb/transaction_handler.h

include/caosdb/value.h

proto

src/caosdb/connection.cpp

src/caosdb/entity.cpp

src/caosdb/transaction.cpp

test/test_data_type.cpp

test/test_entity.cpp