enhance(backend): add unix socket support (#11275)

* unix socket support

* add changelog

* lint

---------

Co-authored-by: syuilo <Syuilotan@yahoo.co.jp>

.config/example.yml

@@ -30,6 +30,10 @@ url: https://example.tld/
 # The port that your Misskey server should listen on.
 port: 3000
 
+# You can also use UNIX domain socket. 
+# socket: /path/to/misskey.sock
+# chmodSocket: '777'
+
 #   ┌──────────────────────────┐
 #───┘ PostgreSQL configuration └────────────────────────────────