feat: integrate with MailJet API for newsletter registration

.env

@@ -40,6 +40,12 @@ MESSENGER_TRANSPORT_DSN=doctrine://default?auto_setup=0
 MAILER_DSN=null://null
 ###< symfony/mailer ###
 
+MAILJET_API_KEY=
+MAILJET_API_SECRET=
+MAILJET_API_BASE_URL=https://api.mailjet.com/v3/REST
+MAILJET_NEWSLETTER_LIST_ID=
+NEWSLETTER_CONFIRMATION_TTL_HOURS=1
+
 APP_BPN_USER=
 APP_BPN_PASSWORD=
 APP_BPN_IP=
@@ -61,6 +67,10 @@ APP_CUSTOMER_SERVICE_EMAIL="[email protected]"
 APP_TRAVEL_PREFER_REMOTE=false
 APP_TRAVEL_ENABLE_FALLBACK=true
 
+# Emails
+APP_DEFAULT_EMAIL_FROM=[email protected]
+APP_DEFAULT_EMAIL_TO=[email protected]
+
 # Booking Configuration
 # Status for new bookings: 'F' (Fixed/Final), 'O' (Option - requires agency confirmation)
 # Use 'O' during beta phase, switch to 'F' for production