Fix performance bar loading issue

What does this MR do?

Related to: #287794 (closed)

Currently the performance bar isn’t working correctly, because we wait until the dom content event. This is triggered after requests have already been sent so we are missing these requests. But I don’t think we need to wait for this event, but not waiting for it could introduce a race condition with app/views/peek/_bar.html.haml, Since now if the DOM isn’t loaded by the time this script is run, we won’t have the #js-peek element

Screenshots (strongly suggested)

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