feat: add grpc export (#2379)

Co-authored-by: Gene Wu <gene.wu@cabital.com>

core/trace/agent.go

@@ -3,12 +3,14 @@ package trace
 import (
 	"context"
 	"fmt"
+	"google.golang.org/grpc"
 	"sync"
 
 	"github.com/zeromicro/go-zero/core/lang"
 	"github.com/zeromicro/go-zero/core/logx"
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/exporters/jaeger"
+	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
 	"go.opentelemetry.io/otel/exporters/zipkin"
 	"go.opentelemetry.io/otel/sdk/resource"
 	sdktrace "go.opentelemetry.io/otel/sdk/trace"
@@ -18,6 +20,7 @@ import (
 const (
 	kindJaeger = "jaeger"
 	kindZipkin = "zipkin"
+	kindGrpc   = "grpc"
 )
 
 var (
@@ -56,6 +59,8 @@ func createExporter(c Config) (sdktrace.SpanExporter, error) {
 		return jaeger.New(jaeger.WithCollectorEndpoint(jaeger.WithEndpoint(c.Endpoint)))
 	case kindZipkin:
 		return zipkin.New(c.Endpoint)
+	case kindGrpc:
+		return otlptracegrpc.NewUnstarted(otlptracegrpc.WithInsecure(), otlptracegrpc.WithEndpoint(c.Endpoint), otlptracegrpc.WithDialOption(grpc.WithBlock())), nil
 	default:
 		return nil, fmt.Errorf("unknown exporter: %s", c.Batcher)
 	}