Describe the bug
Some security headers are missed. Mostly they are important and improve in general the security while using this tool.

General information about the headers: https://owasp.org/www-project-secure-headers/#x-frame-options

To Reproduce
used Firefox Addon: https://addons.mozilla.org/en-US/firefox/addon/cookies-and-headers-analyser/

Expected behavior
secure headers are set

Environment information (please complete the following information):

• Browser: Firefox 88 + Addon
• FreshRSS version: 1.18.0