fix: relative url path for ui mode

[bockstaller]

This is a follow up #29564

I did a deep dive on a redirect issue I observed in my infrastructure and originally attributed to some configuration mistakes on my part. I have code hosted on example.com/code and use subdomain proxying. This leads to the uimode being exposed on example.com/code/proxy/{{port}}.

Clicking on the open uimode link shown by vscode redirected with a 302 to example.com/proxy/{{port}}

The absolute redirect url overruled the relative path handling reverse proxies rely on.

This PR turns the absolute into a relative url to avoid this issue.

[github-actions[bot]]

Test results for "tests 1"

1 failed :x: [firefox-page] › page/network-post-data.spec.ts:109:3 › should get post data for navigator.sendBeacon api calls

7 flaky

:warning: [chromium-library] › library/tracing.spec.ts:243:5 › should not include trace resources from the previous chunks
:warning: [chromium-library] › library/tracing.spec.ts:243:5 › should not include trace resources from the previous chunks
:warning: [chromium-page] › page/interception.spec.ts:104:3 › should intercept network activity from worker
:warning: [firefox-library] › library/tracing.spec.ts:243:5 › should not include trace resources from the previous chunks
:warning: [playwright-test] › ui-mode-test-ct.spec.ts:117:5 › should run component tests after editing test and component
:warning: [playwright-test] › ui-mode-test-screencast.spec.ts:21:5 › should show screenshots
:warning: [webkit-library] › library/tracing.spec.ts:243:5 › should not include trace resources from the previous chunks

26952 passed, 631 skipped :heavy_check_mark::heavy_check_mark::heavy_check_mark:

Merge workflow run.

[bockstaller]

@pavelfeldman I tried to add a test by implementing a proxy in typescript but struggle with the combination of proxying http and ws as well as the multiple testing layers.

Is that something I should invest time in or is continuing without tests ok?

In addition I took a look at tests 1 / ubuntu-22.04 (firefox - Node.js 18) (pull_request) that failure seems like flaky behaviour to me

[github-actions[bot]]

Test results for "tests 1"

2 flaky

:warning: [firefox-page] › page/page-click.spec.ts:850:3 › should not hang when frame is detached
:warning: [chromium-library] › library/trace-viewer.spec.ts:521:1 › should handle multiple headers

27315 passed, 661 skipped :heavy_check_mark::heavy_check_mark::heavy_check_mark:

Merge workflow run.