Added duplicated trigger validation (#3124)

utils/utils.go

@@ -0,0 +1,21 @@
+// Copyright (c) 2016 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package utils
+
+func StringArrayIntersection(arr1, arr2 []string) []string {
+	arrMap := map[string]bool{}
+	result := []string{}
+
+	for _, value := range arr1 {
+		arrMap[value] = true
+	}
+
+	for _, value := range arr2 {
+		if arrMap[value] {
+			result = append(result, value)
+		}
+	}
+
+	return result
+}