Implement Frontend-Only Slow Performance Story

[cstavitsky]

Pass frontendSlowdown=true to trigger a frontend-only slowdown on a new /products-fes (fes = frontend slowdown) page.

• triggers a quick backend products fetch when frontendSlowdown=true is passed, so as to make the http span smaller, and the frontend-only slow span stand out more clearly. See: Add query param to cause frontend-only slowdown #305
• causes slow render problem when frontendSlowdown=true is passed, which creates the frontend-only slow span. See: Create a span that causes frontend-only performance slowdown #273
• triggers a performance issue (this should happen, all the criteria are met for uncompressed asset performance issue; however, it can only be tested at scale so we plan to merge this in)

Examples tested in staging

• Frontend-only slowdown - Pageload transaction
• Frontend-only slowdown - Navigation transaction
• Frontend + Backend slowdown - Pageload transaction - functionality remains the same

Screenshots of Staging

Navigation Transaction for /products-fes

Pageload Transaction for /products-fes

Same as navigation transaction but with browser assets loading and stuff.

Continuing The Frontend-Only Slowdown Story

[cstavitsky]

@ndmanvar I deployed this to staging so you can check it out.

Can you please test:

• the new functionality (1. pass ?frontendSlowdown=true on homepage to make Browse Products point to the frontend-only-slowdown route, 2. visit /products-fes route directly with no query param necessary
• the existing functionality for FE+BE slowdown, to ensure there are no regressions

I already tested, but I definitely want to avoid regressions to our demo data, so please test as well.