Every time I start a project I create a "Walking Skeleton" with all minimum needed configurations. But every time I put inside the skeleton different stuffs. I am wondering now to look for a definition of what exactly a walking skeleton is.
Must a walking skeleton require also deployment steps? Must a walking skeleton require also CI and CD?
There are no universal specifications or requirements for a walking skeleton, that really depends on what is expected from it, which may vary by project and team. Which is most likely the reason for which you find yourself adding different stuff to it for every project.
If you want the walking skeleton to exercise the upcoming project's CI/CD pipeline, then yes, you'll want to add that as well.
Some potentially of interest posts on the DevOps SE site: