When a product changes its name/price in the product catalog, those changes aren't visible in the cart

[bkielbasa]

This is the first time that two components/bounded contexts will communicate in an async way.

For the queue implementation/abstraction, we'll use https://watermill.io/ but will use only Go channels for now as it all works in a single process for now.

The product catalog has to publish the following events:

• ProductNameChanged
• ProductPriceChanged

### Tasks
- [ ] Publish `ProductNameChanged` and `ProductPriceChanged` events in the product catalog
- [ ] Handle `ProductNameChanged` and `ProductPriceChanged` events in the cart module and update carts accordingly