Support ip based auth for nodemailer

[pravi]

nodemailer support secure: true option for ip based auth, so please add SMTP_SECURE: true environment variable which adds secure: true and skips auth options

For now, I could do it by editing config.js, it'd be nice to have it as an environment variable.

diff --git a/config/config.js b/config/config.js
index 21e592d..70398d0 100644
--- a/config/config.js
+++ b/config/config.js
@@ -33,10 +33,7 @@ module.exports = {
     tls: process.env.SMTP_TLS,
     starttls: process.env.SMTP_STARTTLS,
     pgp: process.env.SMTP_PGP ?? true,
-    auth: {
-      user: process.env.SMTP_USER,
-      pass: process.env.SMTP_PASS
-    },
+    secure: true,
     sender: {
       name: process.env.SENDER_NAME,
       email: process.env.SENDER_EMAIL