browser: Implement unroute(url) and unrouteAll

[AgnesToulet]

What?

This PR implements two functions to remove routes that were added using the page.route function:

• page.unroute(url): removes the route(s) that match the same URL (url needs to be exactly what was used in the route function, it can't be a regex that matches the string used in route - this is the behavior of Playwright as well).
• page.unrouteAll(): removes all routes

Note: unroute(url, handler) as in PW will be way harder to implement in the k6 project because of the Sobek layer so this isn't included in this PR. We are waiting for strong interest from users before deciding to look into it.

Why?

This allows users to reset the routes setup during a test or between tests if needed.

Checklist

• I have performed a self-review of my code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have added tests for my changes.
• I have run linter and tests locally (make check) and all pass.

Checklist: Documentation (only for k6 maintainers and if relevant)

Please do not merge this PR until the following items are filled out.

• I have added the correct milestone and labels to the PR.
• I have updated the release notes: link
• I have updated or added an issue to the k6-documentation: grafana/k6-docs#NUMBER if applicable
• I have updated or added an issue to the TypeScript definitions: grafana/k6-DefinitelyTyped#NUMBER if applicable

Related PR(s)/Issue(s)

Closes #4501

[joanlopez]

Looks great!! 🚀 I left a minor suggestion, but it's non-blocking at all.