Add: advanced CI elements to the packaging guide

[lwasser]

We had some discussion around the test lessons and adding content on caching for deps in CI.

see:

• https://github.com/pyOpenSci/python-package-guide/pull/145/files#r1442119731

For simplicity sake - and to keep the page beginner friendly, we decided a more advanced page on CI tips and tricks would be useful to discuss things such as caching that might speed up builds / make builds more efficient.

This issue just captures that conversation so we can move forward with merging the existing tests pr on running tests locally and in ci.