Add the extra call options to grpc calls/streams

gRPC calls should have an extra argument that specifies the "call" options. This will allow to use a specific credentials or add some extra channel parameters(like http2 headers) for the specific call/stream only. The argument should be uninitialized by default.

The signature of the corresponding QAbstractGrpcClient functions should be changed as following:

QGrpcStatus call(QLatin1StringView method, const QProtobufMessage &arg, ReturnType *ret, QGrpcOptions opt = {})

std::shared_ptr<QGrpcCallReply> call(QLatin1StringView method, const QProtobufMessage &arg, QGrpcOptions opt = {})

std::shared_ptr<QGrpcStream> stream(QLatin1StringView method, const QProtobufMessage &arg, QGrpcOptions opt = {})

std::shared_ptr<QGrpcStream> stream(QLatin1StringView method, const QProtobufMessage &arg, const QWeakPointer<ReturnType> ret, QGrpcOptions opt = {})

The QGrpcOptions should be variation of variant map or similar structure, so channels can extract the data that is relevant for them.

It should be possible to read the options back using classes derived from QGrpcOperation.