Observatory related fixes (#788)

* fix:observatory not supported by multi-json

* Fix: observatory starts with empty config & fails to close (#957)

* Update strategy_leastping.go (#1019)

* add custom probe URL support for observatory

* add custom probe interval for observer

* apply coding style

* Fix: observatory log & JSON config(#1211)

Co-authored-by: ihotte <ihotte@yeah.net>

* Change default probe url from api.v2fly.org to www.google.com

* Cherry-pick missing code from branch 'dev-advloadblancer-2'

Co-authored-by: Shelikhoo <xiaokangwang@outlook.com>
Co-authored-by: Loyalsoldier <10487845+Loyalsoldier@users.noreply.github.com>
Co-authored-by: fanyiguan <52657276+fanyiguang@users.noreply.github.com>
Co-authored-by: ihotte <3087168217@qq.com>
Co-authored-by: ihotte <ihotte@yeah.net>

app/observatory/command/command.go

@@ -0,0 +1,50 @@
+// +build !confonly
+
+package command
+
+import (
+	"context"
+
+	"google.golang.org/grpc"
+
+	core "github.com/xtls/xray-core/core"
+	"github.com/xtls/xray-core/app/observatory"
+	"github.com/xtls/xray-core/common"
+	"github.com/xtls/xray-core/features/extension"
+)
+
+type service struct {
+	UnimplementedObservatoryServiceServer
+	v *core.Instance
+
+	observatory extension.Observatory
+}
+
+func (s *service) GetOutboundStatus(ctx context.Context, request *GetOutboundStatusRequest) (*GetOutboundStatusResponse, error) {
+	resp, err := s.observatory.GetObservation(ctx)
+	if err != nil {
+		return nil, err
+	}
+	retdata := resp.(*observatory.ObservationResult)
+	return &GetOutboundStatusResponse{
+		Status: retdata,
+	}, nil
+}
+
+func (s *service) Register(server *grpc.Server) {
+	RegisterObservatoryServiceServer(server, s)
+}
+
+func init() {
+	common.Must(common.RegisterConfig((*Config)(nil), func(ctx context.Context, cfg interface{}) (interface{}, error) {
+		s := core.MustFromContext(ctx)
+		sv := &service{v: s}
+		err := s.RequireFeatures(func(Observatory extension.Observatory) {
+			sv.observatory = Observatory
+		})
+		if err != nil {
+			return nil, err
+		}
+		return sv, nil
+	}))
+}