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

config/initializers/smtp.rb

@@ -2,9 +2,10 @@
 
 require "postal/config"
 
-if Postal.config&.smtp
-  # TODO: by default, we should just send mail through the local Postal
-  # installation rather than having to actually configure an SMTP server.
-  ActionMailer::Base.delivery_method = :smtp
-  ActionMailer::Base.smtp_settings = { address: Postal.config.smtp.host, user_name: Postal.config.smtp.username, password: Postal.config.smtp.password, port: Postal.config.smtp.port || 25 }
-end
+ActionMailer::Base.delivery_method = :smtp
+ActionMailer::Base.smtp_settings = {
+  address: Postal::Config.smtp.host,
+  user_name: Postal::Config.smtp.username,
+  password: Postal::Config.smtp.password,
+  port: Postal::Config.smtp.port
+}