Rewrite documentation examples from yaml to php

Originally posted by @christhomas in https://github.com/cakephp/phinx/issues/1726#issuecomment-724665219

I understand that you wanna get rid of a dependency by moving to plain php, but all the documentation on the cakephp website and that I've found so far is using YAML, so I don't know what a php configuration would look like with all the %%OPTIONS%% etc, etc. I think this change was half baked. You broke a lot of stuff without much explanation and have no way to migrate one to the other, and no documentation updates to reflect that.

Given that the default configuration option is now PHP, it would be good to rewrite all configuration examples to be in PHP. The translation from PHP to YAML / JSON would be left as an exercise to the reader, but given that it's just nested arrays, lists, and strings, should be fairly simple by end-user. Can re-address if this is any issue to people.

Locate the documentation configuration examples and compare them with the now-default PHP configuration described in the issue. Rewrite the examples in PHP, leaving YAML/JSON translation to readers, and verify that all configuration examples consistently reflect the default format.