fix: buffer overrun in the gRPC sample project (open-telemetry#3304)

Building the sample on Windows, the gRPC sample server/client app fails to function correctly. The propagated trace context is corrupted, containing garbage characters after the trace parent string.

The string buffer from gRPC cannot be safely treated as a null-terminated C-string. To ensure safe copying, we must use its length property instead.

Author: lukeina2z

examples/grpc/tracer_common.h

@@ -59,7 +59,7 @@ class GrpcServerCarrier : public opentelemetry::context::propagation::TextMapCar
     auto it = context_->client_metadata().find({key.data(), key.size()});
     if (it != context_->client_metadata().end())
     {
-      return it->second.data();
+      return opentelemetry::nostd::string_view(it->second.data(), it->second.size());
     }
     return "";
   }