Where do original distribution configuration files get stored?

Whenever I do a do-release-upgrade, I usually end up keeping the configuration I have and sometimes make corrections/updates at a later point after testing.

When problems occur upon testing, I compare my current configuration with the distribution's default configuration file.

It would be nice if the do-release-upgrade saved the distribution's default configuration somewhere (e.g., etc/apache/apache.conf.dist), especially in the cases where I choose to override the default with my current configuration.

If the do-release-upgrade does store the original configs, where can I find the distribution default configs?
This would be extremely helpful and any help would be greatly appreciated.

-Lee