MM-22273 New auditing system (phase 1) (#13967)

* New auditing API outputting to syslog via TLS

* New config section for specifying remote syslog server IP, port, and cert.

* Legacy audit API retained for access history feature

audit/const.go

@@ -0,0 +1,20 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package audit
+
+const (
+	DefMaxQueueSize = 1000
+
+	KeyAPIPath   = "api_path"
+	KeyEvent     = "event"
+	KeyStatus    = "status"
+	KeyUserID    = "user_id"
+	KeySessionID = "session_id"
+	KeyClient    = "client"
+	KeyIPAddress = "ip_address"
+
+	Success = "success"
+	Attempt = "attempt"
+	Fail    = "fail"
+)