Update cancel URL handling in HTTP and timer function templates

- Modify header template to use explicit `cancel_url` parameter
- Add `cancel_url` to new timer and HTTP function templates
- Remove default URL fallback in header template

templates/dashboard/http_functions/new.html

@@ -10,6 +10,7 @@ show_logs=False,
 show_client=False,
 show_link=False,
 dashboardUrl=url_for('dashboard_http_functions'),
+cancel_url=url_for('dashboard_http_functions'),
 title='New HTTP Function')
 }}