[offsiteReq] Phase 1: next steps

[agnesgaroux]

RFC: https://github.com/wellcomecollection/docs/blob/main/rfcs/060-offsite-item-requesting/README.md

1. ✅ Determine which combination(s) of Sierra fields:value indicates that an item is held offsite #785
2. ✅ Add DeepStore as a Venue in Prismic, so that it can be indexed in the contentAPI's venue index. Extend the length of the list of NextOpeningDays to accommodate DeepStore's longer leadTimeInDays actually we only care above the next 10 working days #786
3. Update SierraItemUpdater to get the item's location code from Sierra, fetch the corresponding venueOpeningTimes and apply the correct leadTimeInDays. #787
4. Update catalogue-pipeline so that DeepStore items are indexed with the correct locations data #2657

Bonus issue: #788

[jcateswellcome]

part of wellcomecollection/platform#5751