Define goverance changes that the core committers are responsibile for

An example of where we got stuck and went around in circles for months was #3361198: Discuss the futue of the TWG → which we eventually worked around with #3365085: Update the coding standards process on the project page → . However the TWG itself remains an empty working group that is nonetheless represented in the governance documentation and there is no way to change how it works without explicit sign-off from Dries.

This has also come up again with https://www.drupal.org/about/core/blog/request-for-comment-project-updat... → which possibly could have been signed off by a functioning TWG (?) but definitely can't if there isn't one.