Add system console switch for enabling link previews (#5663)

webapp/components/admin_console/admin_sidebar.jsx

@@ -689,6 +689,16 @@ export default class AdminSidebar extends React.Component {
 
                                     }
                                 />
+                                <AdminSidebarSection
+                                    name='link_previews'
+                                    title={
+                                        <FormattedMessage
+                                            id='admin.sidebar.linkPreviews'
+                                            defaultMessage='Link Previews'
+                                        />
+
+                                    }
+                                />
                                 <AdminSidebarSection
                                     name='legal_and_support'
                                     title={