Add a way to choose which of the available shipping methods is selected by default

There should be a way to choose which of all the available configured shipping methods should be selected by default.

It could be either:

  • from the admin side where the shipping methods are configured
  • using the Snipcart API
  • using a tag on the <shipping-rates-list> or on the <shipping-rates-list-item> maybe something like :defaultChecked={rate.slug == "whateverShippingSlug"}