fix SERVER_NAME enforcement in url_for and request.args documentation (#1708)

* 🐛 fix SERVER_NAME enforcement in url_for

fixes #1707

* 💡 add additional documentation for using request.args

fixes #1704

* ✅ add additional test to check url_for without SERVER_NAME

* 📝 add changelog for fixes

sanic/request.py

@@ -519,8 +519,11 @@ class Request:
         :rtype: str
         """
         # Full URL SERVER_NAME can only be handled in app.url_for
-        if "//" in self.app.config.SERVER_NAME:
-            return self.app.url_for(view_name, _external=True, **kwargs)
+        try:
+            if "//" in self.app.config.SERVER_NAME:
+                return self.app.url_for(view_name, _external=True, **kwargs)
+        except AttributeError:
+            pass
 
         scheme = self.scheme
         host = self.server_name