Enable Sentry.tanstackRouterBrowserTracingIntegration by default

[nicohrubec]

We can add this to the integrations for the user from our exported init so the users don't have to manually set this when they have tracing enabled.

Tests:

• Add an E2E test that checks that route tracing works properly.
• Update E2E app to not manually set the integration and check that route tracing still works.

When this is done we also need to update documentation:

• sentry docs: Remove setting the integration from the set up. We also probably no longer need the separate feature page or at least add a note that the integration is now enabled by default.
• in-product onboarding: Remove setting the integration for tracing.

[linear]

JS-1241

[nicohrubec]

Had a look at this today (PR). Since tanstackRouterBrowserTracingIntegration requires an instance of the users router to be passed in we cannot just enable this by default without any action from the user, i.e. we would just swap the line adding the integration for a new router option in the init. I don't think this yields any improvement from a user's perspective so IMO not worth the effort. Closing this for now.