Update protobuf,grpc,etcd dependencies

1. Updated etcd/protobuf/grpc dependencies:

echo "
hack/pin-dependency.sh github.com/golang/protobuf latest
hack/pin-dependency.sh google.golang.org/protobuf latest
hack/pin-dependency.sh go.etcd.io/etcd/api/v3 v3.5.0-rc.0
hack/pin-dependency.sh go.etcd.io/etcd/client/v3 v3.5.0-rc.0
hack/pin-dependency.sh go.etcd.io/etcd/client/pkg/v3 v3.5.0-rc.0
hack/pin-dependency.sh go.etcd.io/etcd/pkg/v3 v3.5.0-rc.0
hack/pin-dependency.sh go.etcd.io/etcd/server/v3 v3.5.0-rc.0
hack/pin-dependency.sh go.etcd.io/etcd/tests/v3 v3.5.0-rc.0
hack/pin-dependency.sh google.golang.org/grpc latest
" | bash

2. Linted transitive dependencies until versions are clean:

hack/lint-dependencies.sh  | grep "  hack/pin-dependency.sh" | bash

3. Linted dependencies until dropped versions are clean:

hack/lint-dependencies.sh  | grep "dropreplace" | bash

4. Updated vendor and internal modules:

hack/update-vendor.sh
hack/update-internal-modules.sh

Repeated steps 2-4 until clean

vendor/github.com/grpc-ecosystem/grpc-gateway/runtime/marshaler.go

@@ -19,6 +19,13 @@ type Marshaler interface {
 	ContentType() string
 }
 
+// Marshalers that implement contentTypeMarshaler will have their ContentTypeFromMessage method called
+// to set the Content-Type header on the response
+type contentTypeMarshaler interface {
+	// ContentTypeFromMessage returns the Content-Type this marshaler produces from the provided message
+	ContentTypeFromMessage(v interface{}) string
+}
+
 // Decoder decodes a byte sequence
 type Decoder interface {
 	Decode(v interface{}) error
@@ -43,6 +50,6 @@ func (f EncoderFunc) Encode(v interface{}) error { return f(v) }
 
 // Delimited defines the streaming delimiter.
 type Delimited interface {
-	// Delimiter returns the record seperator for the stream.
+	// Delimiter returns the record separator for the stream.
 	Delimiter() []byte
 }