feat: new configuration system (and schema) (#2819)

script/smtp_server.rb

@@ -5,5 +5,9 @@ $stderr.sync = true
 
 require_relative "../config/environment"
 
-HealthServer.start(name: "smtp-server", default_port: 9091)
+HealthServer.start(
+  name: "smtp-server",
+  default_port: Postal::Config.smtp_server.default_health_server_port,
+  default_bind_address: Postal::Config.smtp_server.default_health_server_bind_address
+)
 SMTPServer::Server.new(debug: true).run