feat: event aggregator (#6218)

What:
- Event Aggregator Util
- Preparation for normalizing event in a new format (backward compatible with the current format)
- GQL Schema to joiner config and some Entities configured
- Link modules emmiting events

packages/pricing/src/schema/index.ts

@@ -0,0 +1,17 @@
+export const schema = `
+type PriceSet {
+  id: String!
+  money_amounts: [MoneyAmount]
+}
+
+type MoneyAmount {
+  id: String!
+  currency_code: String
+  currency: Currency
+  amount: Float
+  min_quantity: Float
+  max_quantity: Float
+}
+`
+
+export default schema