[MM-14846] Update EditAt for FileIds and Attachment in Post + Ignore FileIds Updates (#10540)

* Set EditAt for FileIds and Attachments; Disallow update/patch of FileIds in API Handler

* Add custom comparison methods for StringArray and Post Attachments

* gofmt

* Split up comparison function to child structs

* Naming consistency

* gofmt

model/utils.go

@@ -36,6 +36,22 @@ type StringInterface map[string]interface{}
 type StringMap map[string]string
 type StringArray []string
 
+func (sa StringArray) Equals(input StringArray) bool {
+
+	if len(sa) != len(input) {
+		return false
+	}
+
+	for index := range sa {
+
+		if sa[index] != input[index] {
+			return false
+		}
+	}
+
+	return true
+}
+
 var translateFunc goi18n.TranslateFunc = nil
 
 func AppErrorInit(t goi18n.TranslateFunc) {