Added windowFunnel aggregate function

Why it matters

The windowFunnel aggregate function allows users to analyze sequences of events over time, making it easier to track user behavior funnels and measure the completion of event sequences within specified time windows.

How to use it

Use the windowFunnel function in your queries by specifying the time window and events sequence you want to analyze. For example, in SQL, apply windowFunnel(time_window, event_column) as an aggregate over your dataset to compute the funnel stages completed within the given time frame.