feat(checkout): CHECKOUT-7918 Update docs around CRUD of gift wrapping for storefront apis

[bc-shawnwang]

CHECKOUT-7674

What changed?

• we can assign a giftWrapping to lineItems using the Storefront API
  • POST /api/storefront/carts
  • POST /api/storefront/carts/{cartId}/items
• we can update an existing giftWrapping using the Storefront API
  • PUT /api/storefront/carts/{cartId}/items/{itemId}
  • PUT /api/storefront/checkouts/{checkoutId}/carts/{cartId}/items/{itemId}
• we can delete an existing giftWrapping using Storefront API (pass giftWrapping: null). if we don't pass giftWrapping, DO NOT CHANGE CURRENT STATUS
  • PUT /api/storefront/carts/{cartId}/items/{itemId}
  • PUT /api/storefront/checkouts/{checkoutId}/carts/{cartId}/items/{itemId}

Anything else?

related PR to add the feature: https://github.com/bigcommerce/bigcommerce/pull/55726

ping @bigcommerce/team-checkout @bigcommerce/dev-docs

[bc-tgomez]

Thanks for the PR @bc-shawnwang! Merging into a DevDocs branch where it'll be merged to main.