Dynamic date offset for funnel insights

Feature request

Problem

When analyzing funnels, users with a conversion window of X days who entered the funnel recently may not have had enough time to complete subsequent steps. This creates a downward bias in conversion rates, as those users are counted as "dropped off" when they are simply still within their conversion window.

The current workaround is to manually set a static end date shifted back by X days (equal to the conversion window). However, this is not dynamic – the insight goes stale and requires manual updates over time.

Solution

Add a "trailing offset" option to funnel insights (and ideally to all insight types), allowing users to define a lag period relative to today. For example:

• Date range: Last 30 days
• Trailing offset: 7 days
• Effective range computed: 37 days ago → 7 days ago
  This would ensure that all users included in the funnel have had at least X days to complete the conversion, producing unbiased and always up-to-date results without any manual intervention.

Debug info

No files, tests, or entry points are named. Start by locating the funnel insights implementation and its date-range handling; done means a trailing offset dynamically shifts the effective range and the behavior is covered for funnel insights, with any broader insight support clearly scoped.