Fix docs about GKE SMTP ports
Update to match current information from GKE saying:
Although port 25 is blocked, you can choose to use port 465, 587, or a non-standard port to send email through a relay.
Update to match current information from GKE saying:
Although port 25 is blocked, you can choose to use port 465, 587, or a non-standard port to send email through a relay.