Adding an example for Next.js (App router)

[Belco90]

Hey there!

I managed to set up MSW in my octochangelog webapp with Next.js (App router) through the instrumentation + instrumentation-client integrations (relevant PR with the changes in case you are curious about it).

I see there was an unsuccessful attempt to add an example for this setup here #101. Would be fine if I create a new PR with an updated example for this setup (requires Next.js v15.3)?

[Belco90]

Nevermind