feat: use a Mailjet sub-account for travel lists

config/services.yaml

@@ -441,6 +441,20 @@ services:
             $defaultListId: '%env(default::MAILJET_DEFAULT_LIST_ID)%'
             $contactMetadataFields: '%mailjet_contact_metadata_fields%'
 
+    # Travel mailing lists live in a Mailjet sub-account, which has its own key pair and keeps
+    # its contacts and lists apart from the newsletter on the main account.
+    app.mailjet.travel_mailing_client:
+        class: App\Mailjet\ApiClient
+        arguments:
+            $apiKey: '%env(default::MAILJET_TRAVEL_MAILING_API_KEY)%'
+            $apiSecret: '%env(default::MAILJET_TRAVEL_MAILING_API_SECRET)%'
+            $apiBaseUrl: '%env(default::MAILJET_API_BASE_URL)%'
+            $contactMetadataFields: '%mailjet_contact_metadata_fields%'
+
+    App\Service\TravelMailingListManager:
+        arguments:
+            $mailjet: '@app.mailjet.travel_mailing_client'
+
     App\EventListener\MaintenanceModeListener:
         arguments:
             $options: