feat(api): add drip campaign (#65148)

Co-authored-by: Oliver Eyton-Williams <ojeytonwilliams@gmail.com>

api/prisma/schema.prisma

@@ -337,3 +337,16 @@ type DailyCodingChallengeApiLanguageChallengeFiles {
   contents String
   fileKey  String
 }
+
+// ----------------------
+
+model DripCampaign {
+  id           String   @id @default(auto()) @map("_id") @db.ObjectId
+  userId       String   @db.ObjectId
+  creationDate DateTime @default(now()) @db.Date
+  email        String
+  variant      String
+
+  @@index([userId], map: "userId_1")
+  @@index([email], map: "email_1")
+}