More details about the new key type can be found here:
https://eff-certbot.readthedocs.io/en/stable/using.html#rsa-and-ecdsa-keys

Existing RSA-based keys will continue to renew as RSA until manual
action is taken. Example from the documentation above:
> certbot renew --key-type ecdsa --cert-name example.com --force-renewal

In the future, we may add a command which does this automatically for
all domains.