Add Browser navigation timing event

[martinkuba]

Changes

This adds a new event for capturing the navigation timing date in browser/web applications.

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• schema-next.yaml updated with changes to existing conventions.

[github-actions]

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[github-actions]

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[trask]

Suggested change

This event captures data from the [Navigation Timing API](https://www.w3.org/TR/navigation-timing-2/). It is recommended to be captured by using the PerformanceObserver API, or when the window load event fires. If the page starts unloading before the page loads, then the partial data can be captured by calling the [performance.getEntriesByType][https://developer.mozilla.org/en-US/docs/Web/API/Performance/getEntriesByType] method.

This event captures data from the [Navigation Timing API](https://www.w3.org/TR/navigation-timing-2/). It is recommended to be captured by using the PerformanceObserver API, or when the window load event fires. If the page starts unloading before the page loads, then the partial data can be captured by calling the [performance.getEntriesByType](https://developer.mozilla.org/en-US/docs/Web/API/Performance/getEntriesByType) method.

[trask]

I'd suggest moving the second sentence to the note (to make the brief shorter)

and maybe add links to the properties in each case, to be super explicit that these are defined externally, e.g. https://www.w3.org/TR/navigation-timing-2/#dom-performancenavigationtiming-domcomplete