[MM-13833] Configured unit tests to log through t.Log (#10272)

* Rerouted the unit test logs through t.Log

* resolving merge confilvts

* Update testing.go

* Update helper_test.go

* Added godocs for NewTestingLogger

* Added go docs for NewTestingLogger

* Resolving conflicts

app/options.go

@@ -4,6 +4,7 @@
 package app
 
 import (
+	"github.com/mattermost/mattermost-server/mlog"
 	"github.com/pkg/errors"
 
 	"github.com/mattermost/mattermost-server/config"
@@ -81,6 +82,13 @@ func StartElasticsearch(s *Server) error {
 	return nil
 }
 
+func SetLogger(logger *mlog.Logger) Option {
+	return func(s *Server) error {
+		s.Log = logger
+		return nil
+	}
+}
+
 type AppOption func(a *App)
 type AppOptionCreator func() []AppOption