feat(external_api) set and cancel private chat through external API

- allow managing chat through API when chat button is not present on UI

modules/API/API.js

 } from '../../react/features/base/conference';
 import { parseJWTFromURLParams } from '../../react/features/base/jwt';
 import JitsiMeetJS, { JitsiRecordingConstants } from '../../react/features/base/lib-jitsi-meet';
-import { pinParticipant } from '../../react/features/base/participants';
+import { pinParticipant, getParticipantById } from '../../react/features/base/participants';
+import { setPrivateMessageRecipient } from '../../react/features/chat/actions';
 import {
     processExternalDeviceRequest
 } from '../../react/features/device-selection/functions';
             } else {
                 logger.error('No recording or streaming session found');
             }
+        },
+        'initiate-private-chat': participantId => {
+            const state = APP.store.getState();
+            const participant = getParticipantById(state, participantId);
+
+            if (participant) {
+                const { isOpen: isChatOpen } = state['features/chat'];
+
+                if (!isChatOpen) {
+                    APP.UI.toggleChat();
+                }
+                APP.store.dispatch(setPrivateMessageRecipient(participant));
+            } else {
+                logger.error('No participant found for the given participantId');
+            }
+        },
+        'cancel-private-chat': () => {
+            APP.store.dispatch(setPrivateMessageRecipient());
         }
     };
     transport.on('event', ({ data, name }) => {

modules/API/external/external_api.js

  */
 const commands = {
     avatarUrl: 'avatar-url',
+    cancelPrivateChat: 'cancel-private-chat',
     displayName: 'display-name',
     e2eeKey: 'e2ee-key',
     email: 'email',
     toggleLobby: 'toggle-lobby',
     hangup: 'video-hangup',
+    intiatePrivateChat: 'initiate-private-chat',
     muteEveryone: 'mute-everyone',
     password: 'password',
     pinParticipant: 'pin-participant',

react/features/chat/middleware.js

 import { MiddlewareRegistry, StateListenerRegistry } from '../base/redux';
 import { playSound, registerSound, unregisterSound } from '../base/sounds';
 import { showToolbox } from '../toolbox/actions';
-import { isButtonEnabled } from '../toolbox/functions';
 
 import { SEND_MESSAGE, SET_PRIVATE_MESSAGE_RECIPIENT } from './actionTypes';
 import { addMessage, clearMessages, toggleChat } from './actions';
  * @returns {void}
  */
 function _addChatMsgListener(conference, store) {
-    if ((typeof APP !== 'undefined' && !isButtonEnabled('chat'))
-        || store.getState()['features/base/config'].iAmRecorder) {
-        // We don't register anything on web if the chat button is not enabled in interfaceConfig
-        // or we are in iAmRecorder mode
+
+    if (store.getState()['features/base/config'].iAmRecorder) {
+        // We don't register anything on web if we are in iAmRecorder mode
         return;
     }