fix(main): filter out frame-ancestors if exists in Content-Security-Policy

[emrahcom]

The application filters out frame-ancestors if it exists in content-security-policy but it doesn't check Content-Security-Policy (with uppercase for the first letter) which is the recommend style in most guides.

In our use-case, we integrate Jitsi with our Keycloak server as identity provider and it uses Content-Security-Policy. So, it doesn't work if the application doesn't have this update.