[0.2.0] Add support for Web Pixel events

[markmur]

What are you trying to accomplish?

Adds support for Web Pixel events

• Swift
• Android

const shopify = useShopifyCheckoutSheet();

useEffect(() => {
  const pixel = shopify.addEventListener('pixel', (event: PixelEvent) => {
      // Dispatch web pixel events to third-party services
      if (hasPermissionToTrack) {
        sendEventToAnalyticsProvider(event);
      }
    },
  );
}, [shopify])

Before you deploy

• I have added tests to support my implementation
• I have read and agree with the contributing documentation readme
• I have read and agree with the code of conduct documentation readme
• I have updated any documentation related to these changes.
• I have updated the README (if applicable).