Update SMTP configuration guide with examples

[thkn-hofa]

Added configuration examples for unauthenticated SMTP in the documentation.

Configuration is different between web/opencve/conf/settings.py and scheduler/airflow.cfg: the first allows to omit username and password variables while the second needs them empty or it throws errors.

[ncrocfer]

Thanks for the PR, the clarification about unauthenticated SMTP is useful 👍

However, duplicating the full configuration just to show the unauthenticated case makes the documentation heavier and harder to maintain.

I think it would be cleaner to keep the existing examples and simply add a comment next to username / password, e.g. leave it empty for unauthenticated SMTP (or must be present but empty for Airflow).

That way we document the behavior without duplicating the whole config block.

[thkn-hofa]

Thanks for the PR, the clarification about unauthenticated SMTP is useful 👍

However, duplicating the full configuration just to show the unauthenticated case makes the documentation heavier and harder to maintain.

I think it would be cleaner to keep the existing examples and simply add a comment next to username / password, e.g. leave it empty for unauthenticated SMTP (or must be present but empty for Airflow).

That way we document the behavior without duplicating the whole config block.

You're right, great input