[StackBlitz dependency]: Upgrade from v6 `react-router-dom` to v7 `react-router`

[GCHQ-Developer-112]

What component is this related to?

StackBlitz component

Why do we need it?

This will keep our StackBlitz code examples up to date and ensure that our components are compatible with v7 react-router. This work is also important now that the react-router-dom package "simply re-exports everything from react-router to smooth the upgrade path for v6 applications".

React Router's guidance on upgrading from v6

🚨 Urgency (low, medium or high)

Low