feat(pricing, types): PriceSets as entry point to pricing module (#4978)

What:
- Adds PriceSet, PriceSetMoneyAmount, updates schema
- Adds service/repo for PriceSet
- Shifts entry point to use PriceSet
- Updates link/joiner config

RESOLVES CORE-1495

packages/pricing/integration-tests/__fixtures__/price-set/data.ts

@@ -0,0 +1,13 @@
+import { CreatePriceSetDTO } from "@medusajs/types"
+
+export const defaultPriceSetsData = [
+  {
+    id: "price-set-1",
+  },
+  {
+    id: "price-set-2",
+  },
+  {
+    id: "price-set-3",
+  },
+] as unknown as CreatePriceSetDTO[]