"Interactive practice" links need to be updated

The [section for interactive practice](https://github.com/bregman-arie/devops-resources#interactive-practice-and-learning-sites) is outdated, as KataKoda is now shut down. Qwiklabs also now points to "Google Cloud Skills Boost" so the wording just needs to be updated.

Open the repository's “Interactive practice and learning sites” section linked in the issue and review its current entries. Remove the shut-down KataKoda reference and update the Qwiklabs wording to “Google Cloud Skills Boost”; the section should no longer contain outdated names or links.

Written by the indexing model from the issue text.