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

config/puma.rb

@@ -1,11 +1,12 @@
 # frozen_string_literal: true
 
 require_relative "../lib/postal/config"
-threads_count = Postal.config.web_server&.max_threads&.to_i || 5
+
+threads_count = Postal::Config.web_server.max_threads
 threads         threads_count, threads_count
-bind_address  = Postal.config.web_server&.bind_address || "127.0.0.1"
-bind_port     = Postal.config.web_server&.port&.to_i || ENV["PORT"] || 5000
+bind_address  = ENV.fetch("BIND_ADDRESS", Postal::Config.web_server.default_bind_address)
+bind_port     = ENV.fetch("PORT", Postal::Config.web_server.default_port)
 bind            "tcp://#{bind_address}:#{bind_port}"
-environment     Postal.config.rails&.environment || "development"
+environment     Postal::Config.rails.environment || "development"
 prune_bundler
 quiet false