PLT-5873 Renamed private groups to private channels (#5924)

* PLT-5873 Renamed private groups to private channels in web app

* PLT-5873 Renamed private groups to private channels in server

webapp/components/integrations/components/abstract_incoming_webhook.jsx

@@ -203,7 +203,7 @@ export default class AbstractIncomingWebhook extends React.Component {
                                 <div className='form__help'>
                                     <FormattedMessage
                                         id='add_incoming_webhook.channel.help'
-                                        defaultMessage='Public channel or private group that receives the webhook payloads. You must belong to the private group when setting up the webhook.'
+                                        defaultMessage='Public or private channel that receives the webhook payloads. You must belong to the private channel when setting up the webhook.'
                                     />
                                 </div>
                             </div>