feat(test): add proxy support for e2e deployment tests (#83118)
### What?
Adds proxy configuration support for e2e deployment tests, allowing test
traffic to be routed through a specified proxy server.
### Why?
Some testing environments require network traffic to be routed through
specific proxy servers or load balancers. This change enables the e2e
deployment test infrastructure to support such configurations by:
- Allowing specification of a proxy IP address via the
`NEXT_TEST_PROXY_ADDRESS` environment variable
- Automatically managing `/etc/hosts` entries to route deployment
domains through the proxy
- Providing proper cleanup when tests complete
