feat(AddPeopleDialog): Enable contact invitation based on interfaceConfig flag

interface_config.js

     DISPLAY_WELCOME_PAGE_CONTENT: true,
     DISPLAY_WELCOME_PAGE_TOOLBAR_ADDITIONAL_CONTENT: false,
 
+    ENABLE_DIAL_OUT: true,
+
     ENABLE_FEEDBACK_ANIMATION: false, // Enables feedback star animation.
 
     FILM_STRIP_MAX_HEIGHT: 120,

react/features/invite/components/add-people-dialog/web/AddPeopleDialog.js

     _dialIn: Object,
 
     /**
-     * Whether or not invite should be hidden.
+     * Whether or not invite contacts should be visible.
      */
-    _hideInviteContacts: boolean,
+    _inviteContactsVisible: boolean,
 
     /**
      * The current url of the conference to be copied onto the clipboard.
 function AddPeopleDialog({
     _conferenceName,
     _dialIn,
-    _hideInviteContacts,
+    _inviteContactsVisible,
     _inviteUrl,
     _liveStreamViewURL,
     _localParticipantName,
             titleKey = 'addPeople.inviteMorePrompt'
             width = { 'small' }>
             <div className = 'invite-more-dialog'>
-                { !_hideInviteContacts && <InviteContactsSection /> }
+                { _inviteContactsVisible && <InviteContactsSection /> }
                 <CopyMeetingLinkSection url = { _inviteUrl } />
                 <InviteByEmailSection
                     inviteSubject = { inviteSubject }
     const { iAmRecorder } = state['features/base/config'];
     const addPeopleEnabled = isAddPeopleEnabled(state);
     const dialOutEnabled = isDialOutEnabled(state);
+    const hideInviteContacts = iAmRecorder || (!addPeopleEnabled && !dialOutEnabled);
 
     return {
         _conferenceName: getRoomName(state),
         _dialIn: state['features/invite'],
-        _hideInviteContacts:
-            iAmRecorder || (!addPeopleEnabled && !dialOutEnabled),
+        _inviteContactsVisible: interfaceConfig.ENABLE_DIAL_OUT && !hideInviteContacts,
         _inviteUrl: getInviteURL(state),
         _liveStreamViewURL:
             currentLiveStreamingSession