in src/main/scala/com/gu/fastly/Lambda.scala [186:192]
def makeMapiSurrogateKey(contentId: String): String = s"Item/$contentId"
def makeDotcomSurrogateKey(contentId: String): String = {
val contentPath = s"/$contentId"
val dotcomSurrogateKey = DigestUtils.md5Hex(contentPath)
dotcomSurrogateKey
}