[SEBA-930] update GRPC version to 1.27 and change kafka message producing

Change-Id: I14145a1351eb2523fa54e66381ad97abc5eedf50
diff --git a/vendor/google.golang.org/grpc/internal/buffer/unbounded.go b/vendor/google.golang.org/grpc/internal/buffer/unbounded.go
index 2cb3109..9f6a0c1 100644
--- a/vendor/google.golang.org/grpc/internal/buffer/unbounded.go
+++ b/vendor/google.golang.org/grpc/internal/buffer/unbounded.go
@@ -26,6 +26,13 @@
 //
 // All methods on this type are thread-safe and don't block on anything except
 // the underlying mutex used for synchronization.
+//
+// Unbounded supports values of any type to be stored in it by using a channel
+// of `interface{}`. This means that a call to Put() incurs an extra memory
+// allocation, and also that users need a type assertion while reading. For
+// performance critical code paths, using Unbounded is strongly discouraged and
+// defining a new type specific implementation of this buffer is preferred. See
+// internal/transport/transport.go for an example of this.
 type Unbounded struct {
 	c       chan interface{}
 	mu      sync.Mutex