Update React Router to v7

[ErlingHauan]

Description

The latest version of React Router (v6.28) triggered console.warn() for updates planned in the next major version (v7), which caused 290 tests to fail. The warnings were as follows:

React Router Future Flag Warning: Relative route resolution within Splat routes is changing in v7. You can use the v7_relativeSplatPath future flag to opt-in early.
React Router Future Flag Warning: React Router will begin wrapping state updates in React.startTransition in v7. You can use the v7_startTransition future flag to opt-in early.

A temporary fix has been added to setupTests.ts:

failOnConsole({
  shouldFailOnWarn: true,
  silenceMessage(message) {
    return /React Router Future Flag Warning/.test(message); // TODO: remove when react router has been updated to v7
  },
});

silenceMessage should be removed once the package has been updated.

Here is an overview of potential code changes.