This PR updates protobuf and grpc to their latest versions. The latest protobuf version no longer requires patches, so we can use it directly from the official Conan Center Index, while the latest grpc still needed a patch, which was added to our own Conan Center Index fork in XRPLF/conan-center-index#8.
The `-Wno-missing-template-arg-list-after-template-kw` flag is only needed for the grpc library. Use `+=` for the default build flags to make it easier to extend in the future.
Co-authored-by: Bart Thomee <11445373+bthomee@users.noreply.github.com>
