controller: removes all panics from extension server (envoyproxy#1610)

**Description**

This removes all panics from extension server code paths, mostly for
making it resilient against any bad input from EG

---------

Signed-off-by: Takeshi Yoneda <[email protected]>
Co-authored-by: Ignasi Barrera <[email protected]>

Author: mathetake

internal/extensionserver/extensionserver.go

@@ -7,12 +7,15 @@ package extensionserver
 
 import (
 	"context"
+	"fmt"
 
 	egextension "github.com/envoyproxy/gateway/proto/extension"
 	"github.com/go-logr/logr"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/health/grpc_health_v1"
 	"google.golang.org/grpc/status"
+	"google.golang.org/protobuf/proto"
+	"google.golang.org/protobuf/types/known/anypb"
 	"sigs.k8s.io/controller-runtime/pkg/client"
 )
 
@@ -51,3 +54,16 @@ func (s *Server) List(context.Context, *grpc_health_v1.HealthListRequest) (*grpc
 		serverName: {Status: grpc_health_v1.HealthCheckResponse_SERVING},
 	}}, nil
 }
+
+// toAny marshals the provided message to an Any message.
+func toAny(msg proto.Message) (*anypb.Any, error) {
+	b, err := proto.Marshal(msg)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal message to Any: %w", err)
+	}
+	const envoyAPIPrefix = "type.googleapis.com/"
+	return &anypb.Any{
+		TypeUrl: envoyAPIPrefix + string(msg.ProtoReflect().Descriptor().FullName()),
+		Value:   b,
+	}, nil
+}