Document how to use GitLab registry with yarn v2

We have some information about publishing/installing packages to/from GitLab NPM registry with yarn. It is scattered through this page: https://docs.gitlab.com/ee/user/packages/npm_registry/

There is yarn v2 which at first glance seems to be different from the Classic one and I think we should have some examples on how to set that up with our registry as well.

Ticket: 193994

Agent: Kate Grechishkina