protobuf: remove gogoproto

Removes gogo/protobuf from buildx and updates to a version of
moby/buildkit where gogo is removed.

This also changes how the proto files are generated. This is because
newer versions of protobuf are more strict about name conflicts. If two
files have the same name (even if they are relative paths) and are used
in different protoc commands, they'll conflict in the registry.

Since protobuf file generation doesn't work very well with
`paths=source_relative`, this removes the `go:generate` expression and
just relies on the dockerfile to perform the generation.

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

vendor/golang.org/x/crypto/ssh/server.go

@@ -462,6 +462,24 @@ func (p *PartialSuccessError) Error() string {
 // It is returned in ServerAuthError.Errors from NewServerConn.
 var ErrNoAuth = errors.New("ssh: no auth passed yet")
 
+// BannerError is an error that can be returned by authentication handlers in
+// ServerConfig to send a banner message to the client.
+type BannerError struct {
+	Err     error
+	Message string
+}
+
+func (b *BannerError) Unwrap() error {
+	return b.Err
+}
+
+func (b *BannerError) Error() string {
+	if b.Err == nil {
+		return b.Message
+	}
+	return b.Err.Error()
+}
+
 func (s *connection) serverAuthenticate(config *ServerConfig) (*Permissions, error) {
 	sessionID := s.transport.getSessionID()
 	var cache pubKeyCache
@@ -734,6 +752,18 @@ userAuthLoop:
 			config.AuthLogCallback(s, userAuthReq.Method, authErr)
 		}
 
+		var bannerErr *BannerError
+		if errors.As(authErr, &bannerErr) {
+			if bannerErr.Message != "" {
+				bannerMsg := &userAuthBannerMsg{
+					Message: bannerErr.Message,
+				}
+				if err := s.transport.writePacket(Marshal(bannerMsg)); err != nil {
+					return nil, err
+				}
+			}
+		}
+
 		if authErr == nil {
 			break userAuthLoop
 		}