chore: API fixes (#3014)

- Minor API fixes
- Configuration screen for LINE inbox

app/javascript/shared/mixins/inboxMixin.js

@@ -5,6 +5,7 @@ export const INBOX_TYPES = {
   TWILIO: 'Channel::TwilioSms',
   API: 'Channel::Api',
   EMAIL: 'Channel::Email',
+  LINE: 'Channel::Line',
 };
 
 export default {
@@ -27,6 +28,9 @@ export default {
     isATwilioChannel() {
       return this.channelType === INBOX_TYPES.TWILIO;
     },
+    isALineChannel() {
+      return this.channelType === INBOX_TYPES.LINE;
+    },
     isAnEmailChannel() {
       return this.channelType === INBOX_TYPES.EMAIL;
     },