Add option to control WebUI clickjacking protection

Some users actually want embedding WebUI into their custom build iframe.
Closes #7370.

src/base/preferences.h

@@ -194,6 +194,10 @@ public:
     QString getWebUiPassword() const;
     void setWebUiPassword(const QString &new_password);
 
+    // WebUI security
+    bool isWebUiClickjackingProtectionEnabled() const;
+    void setWebUiClickjackingProtectionEnabled(bool enabled);
+
     // HTTPS
     bool isWebUiHttpsEnabled() const;
     void setWebUiHttpsEnabled(bool enabled);