feat: add support for sending email to the docker image

docker/env.example

@@ -1,10 +1,25 @@
 # Password for the database superuser
 DB_PASSWORD=...
 
+# SMTP - Outgoing server
+SMTP_HOST=smtp.example.org
+# SMTP - Port number
+SMTP_PORT=587
+# SMTP - Enable TLS? (on/off)
+SMTP_TLS=on
+# SMTP - Authenticate to outgoing server? (on/off)
+SMTP_AUTH=on
+# SMTP - User name
+SMTP_USER=...
+# SMTP - Password
+SMTP_PASSWORD=...
+
 # URL of the static assets from an external perspective
 LW_STATIC_URL=http://localhost/static
 # Send email? (yes or no)
 LW_SEND_MAIL=no
+# Source address for LW mails
+LW_MAIL_FROM=legacyworlds@example.org
 
 # Legacyworlds database - Main user
 LW_DB_USER_PASS=...