added manger to keep track of go routines in the services (#2869)

- added manager to wait for all go routines to end before exit
- code refactor
- renamed Manafer to Interface and GoRoutineManager to GroupManager
- replaced some go routine calls with manager Add func
- added unit tests for manager

pkg/utils/metrics/server.go

@@ -26,9 +26,10 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/metrics"
 
 	"github.com/fission/fission/pkg/utils/httpserver"
+	"github.com/fission/fission/pkg/utils/manager"
 )
 
-func ServeMetrics(ctx context.Context, parent string, logger *zap.Logger) {
+func ServeMetrics(ctx context.Context, parent string, logger *zap.Logger, mgr manager.Interface) {
 	metricsAddr := os.Getenv("METRICS_ADDR")
 	if metricsAddr == "" {
 		metricsAddr = "8080"
@@ -45,5 +46,5 @@ func ServeMetrics(ctx context.Context, parent string, logger *zap.Logger) {
 			EnableOpenMetrics: true,
 		},
 	))
-	httpserver.StartServer(ctx, logger, parent+"/metrics", metricsAddr, mux)
+	httpserver.StartServer(ctx, logger, mgr, parent+"/metrics", metricsAddr, mux)
 }