Update to react-router v6

[joey-grafana]

Part of a larger initiative.

"Starting from Grafana 10, plugins can start using the v6 of react-router. Overall, react-router v6 aims to simplify route configuration and provide a more flexible and intuitive API for developers."

"We are going to deprecate using react-router v5 in plugins from Grafana 11, and we would like to make sure our internal app plugins are using the v6 version by the time we finish migrating Grafana core itself."