feat: yarn 2 (#5657)

* feat: yarn 2

* Apply suggestions from code review

Co-Authored-By: Michael Kriese <michael.kriese@visualon.de>

* refactor: move yarnMajorVersion test

* test: apply patch from @JamieMagee

see https://github.com/renovatebot/renovate/pull/5657#issuecomment-611205192



* test: update snapshots

* prettier-fix

Co-authored-by: Michael Kriese <michael.kriese@visualon.de>
Co-authored-by: Jamie Magee <jamie.magee@gmail.com>