Made the SMTP server config env-driven (#56)

Author: PianoNic

realms/schuly-realm.json

@@ -7,14 +7,14 @@
   "verifyEmail": true,
   "registrationFlow": "registration",
   "smtpServer": {
-    "host": "smtp.resend.com",
-    "port": "2465",
-    "ssl": "true",
-    "starttls": "false",
+    "host": "${env.SMTP_HOST}",
+    "port": "${env.SMTP_PORT}",
+    "ssl": "${env.SMTP_SSL}",
+    "starttls": "${env.SMTP_STARTTLS}",
     "auth": "true",
-    "user": "resend",
+    "user": "${env.SMTP_USER}",
     "password": "${env.SMTP_PASSWORD}",
-    "from": "noreply@schuly.dev",
+    "from": "${env.SMTP_FROM}",
     "fromDisplayName": "Schuly"
   },
   "resetPasswordAllowed": true,