MM-36764 mlog refactor (#18118)

Refactor mlog
- simplify mlog by removing redundant code
- remove Zap dependency
- update unit test helpers
- update logging config
- update auditing

einterfaces/mocks/MetricsInterface.go

@@ -5,7 +5,7 @@
 package mocks
 
 import (
-	logr "github.com/mattermost/logr"
+	logr "github.com/mattermost/logr/v2"
 	mock "github.com/stretchr/testify/mock"
 
 	model "github.com/mattermost/mattermost-server/v6/model"