App router migration new relic configuration

[boodland]

Children PR for the progressive migration of _app.tsx and _document.tsx within the Root Layout

Issue link / number: #1083

What changes did you make? Created new relic configuration Added new relic configuration to root layout

Why did you make the changes? In order to be able to have new relic within app router

Did you run tests? Yes

Navigate to http://localhost:3000/public-route-test to check that the head nr-browser-agent and body scripts are added properly