DefaultUpdateWebhook and Item do not use the ItemId schema for their item_id fields

[relsunkaev]

The #/components/schemas/DefaultUpdateWebhook and #/components/schemas/Item are not using the #/components/schemas/ItemId schema for their respective item_id fields. Since I'm assuming the reason ItemId has a schema at all is to be able to modify what an ItemId looks like in one place this might be worth fixing.

[phoenixy1]

This is intentional for the second one -- we sometimes do this because it in different contexts the same field needs a different description and there isn't a good way to do that via a shared ref in OpenAPI (not that I was able to find, anyway). I agree that DefaultUpdateWebhook probably could use the ItemId schema, though.