Migrate all Internal projects, groups, and snippets on GitLab.com to Private

Overview

In https://gitlab.com/gitlab-org/gitlab-ee/issues/12388, we disabled the "Internal" visibility setting on GitLab.com since it's confusing and almost indistinguishable from setting a resource to Public. This only applies to new projects, groups, and snippets and any existing Internal resources remain Internal.

Proposal

Migrate remaining Internal projects, groups, and snippets to Private on GitLab.com.