Add strict_increase option to windowFunnel function

Why it matters

This feature addresses the problem of duplicate event counting within the windowFunnel function, ensuring more accurate funnel analysis by calculating each event strictly once. It solves issue #21835, improving result correctness for users performing event sequence analysis.

How to use it

To use the feature, specify the strict_increase parameter in the windowFunnel function call. This will enforce strict event counting so that each event contributes only once to the funnel calculation. For example:

SELECT windowFunnel(60, event, user, windowFunnelMaxSteps, strict_increase = 1) FROM ...