Add Infiltrator's Shroud (?)

[rdw-software]

It's unclear whether this is a rare drop or guaranteed. Unless it's a 100% drop, the item should likely be added. Link:

• https://www.wowhead.com/item=226810/infiltrators-shroud

---

Split off from #734.

[rdw-software]

Looks like the drop is more or less guaranteed (88% on wowhead). No point in tracking it.