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

app/views/app_mailer/server_send_limit_approaching.text.erb

@@ -13,5 +13,5 @@ You can view more information about this server at:
 
 Thanks,
 
-<%= Postal.smtp_from_name %>
-<%= Postal.smtp_from_address %>
+<%= Postal::Config.smtp.from_name %>
+<%= Postal::Config.smtp.from_address %>