MM-23222 mirror audit logs to file (#14062)

* MM-23222 add file target (with rotation) to audit

* MM-23222 mirror syslog audits to local filesystem

    * provides config options for file name, max size, max age

    * rotates files based on max size and max age; delete as needed based on max backups

* include cluster id in log records

* sort meta data fields

audit/audit_test.go

@@ -0,0 +1,67 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package audit
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"github.com/wiggin77/logr"
+	"github.com/wiggin77/logr/format"
+)
+
+func Test_sortAuditFields(t *testing.T) {
+	type args struct {
+		fields logr.Fields
+	}
+	tests := []struct {
+		name string
+		args args
+		want []format.ContextField
+	}{
+		{name: "empty list",
+			args: args{fields: logr.Fields{}},
+			want: []format.ContextField{},
+		},
+		{name: "partial list",
+			args: args{fields: logr.Fields{"zProp": "x", "xProp": "x", "yProp": "x", KeyClusterID: "x", KeyEvent: "x"}},
+			want: []format.ContextField{
+				{Key: KeyEvent, Val: "x"},
+				{Key: "xProp", Val: "x"},
+				{Key: "yProp", Val: "x"},
+				{Key: "zProp", Val: "x"},
+				{Key: KeyClusterID, Val: "x"},
+			},
+		},
+		{name: "append/prepend only list",
+			args: args{fields: logr.Fields{KeyClusterID: "x", KeyEvent: "x", KeySessionID: "x", KeyIPAddress: "x", KeyClient: "x",
+				KeyUserID: "x", KeyStatus: "x"}},
+			want: []format.ContextField{
+				// prepend: KeyEvent, KeyStatus, KeyUserID, KeySessionID, KeyIPAddress
+				// append: KeyClusterID, KeyClient
+				{Key: KeyEvent, Val: "x"},
+				{Key: KeyStatus, Val: "x"},
+				{Key: KeyUserID, Val: "x"},
+				{Key: KeySessionID, Val: "x"},
+				{Key: KeyIPAddress, Val: "x"},
+				{Key: KeyClusterID, Val: "x"},
+				{Key: KeyClient, Val: "x"},
+			},
+		},
+		{name: "sortables only list",
+			args: args{fields: logr.Fields{"zProp": "x", "xProp": "x", "yProp": "x"}},
+			want: []format.ContextField{
+				{Key: "xProp", Val: "x"},
+				{Key: "yProp", Val: "x"},
+				{Key: "zProp", Val: "x"},
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := sortAuditFields(tt.args.fields)
+			require.Equal(t, tt.want, got)
+		})
+	}
+}