Add a child span to the grpc e2e test for the server

[MrAlias]

To ensure we are correctly tracking the span in the server probe, we should add a child span (i.e. an HTTP or OTel global span), that will be instrumented with the auto project, to ensure that child correctly gets the server span as its parent.

opentelemetry-go-instrumentation/internal/test/e2e/grpc/main.go

Lines 29 to 35 in d447af1

	func (s *server) SayHello(ctx context.Context, in *pb.HelloRequest) (*pb.HelloReply, error) {
	log.Printf("Received: %v", in.GetName())
	if in.GetName() == "unimplemented" {
	return nil, status.Error(codes.Unimplemented, "unimplmented")
	}
	return &pb.HelloReply{Message: "Hello " + in.GetName()}, nil
	}