Add single link/unlink commands for gitlab-ui [ci-skip]

What does this MR do?

add yarn link-gitlab-ui and yarn unlink-gitlab-ui

Part 2 of #219713

Depends on gitlab-development-kit!1285 (merged) (checkout that branch and run make update in gdk root folder)

Why?

unlink automatically runs yarn --force afterward so you don't always have to do it yourself
typing @ is tedious