[APIv4] add getChannelMembersTimezone (#9286)

* add getChannelMembersTimezone

* update per feedback review

* add delimeter to error

model/utils.go

@@ -564,3 +564,26 @@ func IsDomainName(s string) bool {
 
 	return ok
 }
+
+func RemoveDuplicateStrings(in []string) []string {
+	out := []string{}
+	seen := make(map[string]bool, len(in))
+
+	for _, item := range in {
+		if !seen[item] {
+			out = append(out, item)
+
+			seen[item] = true
+		}
+	}
+
+	return out
+}
+
+func GetPreferredTimezone(timezone StringMap) string {
+	if timezone["useAutomaticTimezone"] == "true" {
+		return timezone["automaticTimezone"]
+	}
+
+	return timezone["manualTimezone"]
+}