[react] implement poor FID web vital

[cstavitsky]

FID measures the time from when a user first interacts with a page (that is, when they click a link, tap on a button, or use a custom, JavaScript-powered control) to the time when the browser is actually able to begin processing event handlers in response to that interaction.

Create an opt-in scenario in the /products transaction that causes a poor FID web vital.

• If the query parameter ?webvital=fid is used, the scenario should trigger. If the query param is not used, then poor FID should not trigger. (refer to other usage of query parameters within the demo app, like ?se= representing a given solutions engineer.)
• the user interaction that should trigger poor FID should be, clicking on the "Add To Cart" button for a given Product.
• Communicate in the PR an accompanying narrative of, "this is what we could do to fix the slow FID"