add support for :authority pseudo-header for grpc client

This adds support for configuring `authority` dial option for grpc exporter

Author: enuret

config/configgrpc/configgrpc.go

@@ -86,6 +86,10 @@ type GRPCClientSettings struct {
 	// https://github.com/grpc/grpc-go/blob/master/examples/features/load_balancing/README.md
 	BalancerName string `mapstructure:"balancer_name"`
 
+	// WithAuthority parameter configures client to rewrite ":authority" header
+	// (godoc.org/google.golang.org/grpc#WithAuthority)
+	Authority string `mapstructure:"authority"`
+
 	// Auth configuration for outgoing RPCs.
 	Auth *configauth.Authentication `mapstructure:"auth"`
 }
@@ -247,6 +251,10 @@ func (gcs *GRPCClientSettings) toDialOptions(host component.Host, settings compo
 		opts = append(opts, grpc.WithDefaultServiceConfig(fmt.Sprintf(`{"loadBalancingPolicy":"%s"}`, gcs.BalancerName)))
 	}
 
+	if gcs.Authority != "" {
+		opts = append(opts, grpc.WithAuthority(gcs.Authority))
+	}
+
 	otelOpts := []otelgrpc.Option{
 		otelgrpc.WithTracerProvider(settings.TracerProvider),
 		otelgrpc.WithMeterProvider(settings.MeterProvider),

config/configgrpc/configgrpc_test.go

@@ -80,6 +80,7 @@ func TestAllGrpcClientSettings(t *testing.T) {
 				WriteBufferSize: 1024,
 				WaitForReady:    true,
 				BalancerName:    "round_robin",
+				Authority:       "pseudo-authority",
 				Auth:            &configauth.Authentication{AuthenticatorID: component.NewID("testauth")},
 			},
 			host: &mockHost{
@@ -108,6 +109,7 @@ func TestAllGrpcClientSettings(t *testing.T) {
 				WriteBufferSize: 1024,
 				WaitForReady:    true,
 				BalancerName:    "round_robin",
+				Authority:       "pseudo-authority",
 				Auth:            &configauth.Authentication{AuthenticatorID: component.NewID("testauth")},
 			},
 			host: &mockHost{
@@ -136,6 +138,7 @@ func TestAllGrpcClientSettings(t *testing.T) {
 				WriteBufferSize: 1024,
 				WaitForReady:    true,
 				BalancerName:    "round_robin",
+				Authority:       "pseudo-authority",
 				Auth:            &configauth.Authentication{AuthenticatorID: component.NewID("testauth")},
 			},
 			host: &mockHost{
@@ -149,7 +152,7 @@ func TestAllGrpcClientSettings(t *testing.T) {
 		t.Run(test.name, func(t *testing.T) {
 			opts, err := test.settings.toDialOptions(test.host, tt.TelemetrySettings)
 			assert.NoError(t, err)
-			assert.Len(t, opts, 9)
+			assert.Len(t, opts, 10)
 		})
 	}
 }