Move asdf-yarn to here

[kroleg]

• current main contributor (@canterberry) is not interested in maintaining anymore but agreed to help with moving to asdf-community (see Transfer plugin to asdf-community twuni/asdf-yarn#37)
• i've created a PR in infra repo: Add asdf-yarn infrastructure#160

[kroleg]

Alternative might be to switch to https://github.com/mise-plugins/asdf-yarn. I see that pkl plugin is doing that https://github.com/asdf-vm/asdf-plugins/blob/master/plugins/pkl