test(tanstackstart-react): Set up E2E test application

[github-actions]

Note

The pull request "test(tanstackstart-react): Set up E2E test application" was created by @nicohrubec but did not reference an issue. Therefore this issue was created for better visibility in external tools like Linear.

This sets up a basic E2E test for the Tanstack Start React SDK.

For now I have added the following three tests:

• An error thrown directly on the client is automatically captured.
• An error thrown from a server side function is automatically captured. I am not sure why this works atm, but probably this is somehow propagated to the frontend.
• An error thrown from a server route is only captured if we manually instrument it with Sentry.captureException.

[linear]

JS-1248