fix: re-add reconnect: true to database

This is deprecated and, in my tests, isn't needed but to avoid any
potential issues I am re-adding it here. When we upgrade to Rails 7.1,
we can remove this and that'll handle reconnections as appropriate.

config/database.yml

@@ -1,5 +1,6 @@
 default: &default
   adapter: mysql2
+  reconnect: true
   encoding: <%= Postal.config.main_db.encoding %>
   pool: <%= Postal.config.main_db.pool_size %>
   username: <%= Postal.config.main_db.username %>