As a Watchlist Expiry user, I want expiry parameters enabled when adding items to the watchlist via the API, so the feature can be accessed via the API.
Background: This ticket is for back-end work only.
- When adding an item to the watchlist through the API, add a parameter for expiry so the item can be added with an expiration.
- Note: there is *one* expiry value allowed, even for bulk additions. Whatever is supplied, all added items will receive the same expiry value.