Provide more context for `deleteExpiredOrdersAfter`, `expireOrdersAfter`

[korycins]

We should provide a chapter/section which will explain, how expireOrdersAfter and deleteExpiredOrdersAfter https://docs.saleor.io/docs/3.x/api-reference/miscellaneous/objects/order-settings#

expireOrdersAfter - the value in minutes after unpaid orders will be marked as expired. deleteExpiredOrdersAfter - the flag in days, after expired orders will be deleted from Saleor.