Fixed visible 'HTTP response headers' in 'System settings'

[Limraj]

To Reproduce Steps to reproduce the behavior:

1. Login as admin;
2. Go to 'System settings';
3. Find section 'HTTP settings' and text field 'HTTP response headers';
4. Past:

{
  "Content-Security-Policy" : "default-src 'self';style-src 'unsafe-inline' 'self';script-src 'unsafe-inline' 'unsafe-eval' 'self';"
}

5. Click on 'Save' button:

6. Refresh page then: We see [object Object] instead of text from step 4 -> error

Spec:

• Scada-LTS version: v2.7.7
• Chrome version: 122.0.6261.95