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

[nicohrubec]

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.

Closes #18265

[github-actions]

node-overhead report 🧳

Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	9,113	-	9,036	+1%
GET With Sentry	1,716	19%	1,738	-1%
GET With Sentry (error only)	6,135	67%	6,057	+1%
POST Baseline	1,192	-	1,193	-0%
POST With Sentry	583	49%	593	-2%
POST With Sentry (error only)	1,048	88%	1,061	-1%
MYSQL Baseline	3,320	-	3,354	-1%
MYSQL With Sentry	451	14%	456	-1%
MYSQL With Sentry (error only)	2,676	81%	2,727	-2%

View base workflow run

[andreiborza]

LGTM