Feature: mailcow widget (#3993)

---------

Co-authored-by: shamoon <4887959+shamoon@users.noreply.github.com>

docs/widgets/services/mailcow.md

@@ -0,0 +1,15 @@
+---
+title: Mailcow
+description: Mailcow Widget Configuration
+---
+
+Learn more about [Mailcow](https://github.com/mailcow/mailcow-dockerized).
+
+Allowed fields: `["domains", "mailboxes", "mails", "storage"]`.
+
+```yaml
+widget:
+  type: mailcow
+  url: https://mailcow.host.or.ip
+  key: mailcowapikey
+```