Use protobuf reflection for serialization

This is used instead of regular Go relection because it is harder
to map it to the table schema. The protobuf is the canonical
representation making converison easier.

tools/mc2bq/pkg/export/export.go

@@ -30,6 +30,7 @@ import (
 	"golang.org/x/sync/errgroup"
 	"google.golang.org/api/iterator"
 	"google.golang.org/api/option"
+	"google.golang.org/protobuf/reflect/protoreflect"
 
 	"github.com/GoogleCloudPlatform/migrationcenter-utils/tools/mc2bq/pkg/gapiutil"
 	"github.com/GoogleCloudPlatform/migrationcenter-utils/tools/mc2bq/pkg/mcutil"
@@ -187,7 +188,7 @@ type iterable[T any] interface {
 	Next() (T, error)
 }
 
-type objectReader[T any] struct {
+type objectReader[T protoreflect.ProtoMessage] struct {
 	schema     bigquery.Schema
 	it         iterable[T]
 	serializer func(obj T) ([]byte, error)
@@ -197,9 +198,9 @@ type objectReader[T any] struct {
 	bytesRead   uint64
 }
 
-func newObjectReader[T any](it iterable[*T], root string, schema bigquery.Schema) *objectReader[*T] {
-	return &objectReader[*T]{
-		serializer: exporterschema.NewSerializer[*T](root, schema),
+func newObjectReader[T protoreflect.ProtoMessage](it iterable[T], root string, schema bigquery.Schema) *objectReader[T] {
+	return &objectReader[T]{
+		serializer: exporterschema.NewSerializer[T](root, schema),
 		it:         it,
 		schema:     schema,
 	}
@@ -247,7 +248,7 @@ func (r *objectReader[T]) Read(buf []byte) (int, error) {
 	return n, nil
 }
 
-func newMigrationCenterLoadSource[T any](r *objectReader[T]) bigquery.LoadSource {
+func newMigrationCenterLoadSource[T protoreflect.ProtoMessage](r *objectReader[T]) bigquery.LoadSource {
 	// Creating a full blown bigquery.LoadSource requires a lot of low level big query operations.
 	// To save on time we create a ReaderSource and feed it the assets as a json stream.
 	src := bigquery.NewReaderSource(r)

tools/mc2bq/pkg/export/v1.go

@@ -36,7 +36,7 @@ func (mc *MCv1) AssetSource(ctx context.Context, pal mcutil.ProjectAndLocation)
 		Parent:   pal.String(),
 		PageSize: 1000,
 	})
-	r := newObjectReader[migrationcenterpb.Asset](it, "asset", mc.schema.AssetTable)
+	r := newObjectReader[*migrationcenterpb.Asset](it, "asset", mc.schema.AssetTable)
 	src := newMigrationCenterLoadSource(r)
 	return &struct {
 		bigquery.LoadSource
@@ -49,7 +49,7 @@ func (mc *MCv1) GroupSource(ctx context.Context, pal mcutil.ProjectAndLocation)
 		Parent:   pal.String(),
 		PageSize: 1000,
 	})
-	r := newObjectReader[migrationcenterpb.Group](it, "asset", mc.schema.GroupTable)
+	r := newObjectReader[*migrationcenterpb.Group](it, "group", mc.schema.GroupTable)
 	src := newMigrationCenterLoadSource(r)
 	return &struct {
 		bigquery.LoadSource
@@ -62,7 +62,7 @@ func (mc *MCv1) PreferenceSetSource(ctx context.Context, pal mcutil.ProjectAndLo
 		Parent:   pal.String(),
 		PageSize: 1000,
 	})
-	r := newObjectReader[migrationcenterpb.PreferenceSet](it, "asset", mc.schema.PreferenceSetTable)
+	r := newObjectReader[*migrationcenterpb.PreferenceSet](it, "preference_set", mc.schema.PreferenceSetTable)
 	src := newMigrationCenterLoadSource(r)
 	return &struct {
 		bigquery.LoadSource