Add App Directory link to Integrations pages (#6731)

* Update installed_commands.jsx

* Update installed_incoming_webhooks.jsx

* Update installed_oauth_apps.jsx

* Update installed_outgoing_webhooks.jsx

* Update integrations.jsx

* Update quick_switch_modal.jsx

* Update en.json

* Decrease help text size in Integrations page

* Fix syntax error

* Tweak help text size based on Asaad's feedback

* Fix indentation

* Update help text classname to backstage-list__help

* Update _backstage.scss

* Remove the horizontal line in integrations page

* Renamed template strings for integrations help links

webapp/sass/routes/_backstage.scss

@@ -209,7 +209,7 @@
 
 .backstage-list__help {
     display: block;
-    padding: 1em 0;
+    margin: 1em 0;
 }
 
 .backstage-list__item {