Draft: Fix Settings UI

# Description Previously, the settings page would show the browser's current runtime state rather than what we just saved in auto-config.lisp. This was confusing as it made it appear that settings weren't being saved. - Add get-configured-value to read values from auto-config - Update all settings controls to check saved values first - Migrate cookie policy and zoom to use define-configuration - Make configure-slot to generate modern define-configuration forms (just in case, I am not sure if it's needed) # Checklist: - [ ] Git branch state is mergable. - It isn't, as it is based on my other changes, not master - Also the changes are a little dirty, I'd like to discuss the issue a bit - [ ] Changelog is up to date (via a separate commit). - [x] New dependencies are accounted for. - [x] Documentation is up to date. - [x] Compilation and tests (`(asdf:test-system :nyxt/<renderer>)`) - No new compilation warnings. - Tests are sufficient.