Update `waitForNetworkIdle()` docblock

[bert-w]

Summary Documentation update for page.waitForNetworkIdle(). The original documentation did not mention anything about a failing promise, and if/how that would ever happen.

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[OrKoN]

@jrandolf could you please include this change into one of your documentation changes? I think we can improve this part of the docs but we actually need to document the options inline and have @defaultValue for default values etc.

[OrKoN]

Closed due to lack of activity.