Support exclusion criteria in experiment exposure

[andehen]

Feature request

Is your feature request related to a problem?

A customer is running an experiment that moves their sign-up stage later in the funnel to measure its impact on new customer acquisition. However, they need to exclude users who log in at that stage, as they are already existing customers. Currently, there is no built-in way to filter out those users, which can affect the accuracy of experiment results.

Describe the solution you'd like

Introduce exclusion criteria in experiment exposure. This would allow teams to filter out users based on specific behaviors (e.g., logging in), ensuring that only relevant users are included in the experiment.

Additional context

Zendesk ticket https://posthoghelp.zendesk.com/agent/tickets/25834