Feature Request: Allow "setPersonPropertiesForFlags" options to used in feature flag matching rules

Feature request

Is your feature request related to a problem?

• A bit of a corollary to https://github.com/PostHog/posthog/issues/67928
• We have options to set overrides on feature flags on a specific user.
• However, these properties aren't captured and displayed in the feature flag matching rules.
• These ephemeral properties make it difficult to create flag matching criteria.

Describe the solution you'd like

• It would be great if data for these events would populate the match criteria for feature flags.
• This would include things like setPersonPropertiesForFlags & setPersonProperties.
• This would allow people to create these match rules without forcing a new event to be processed.

Describe alternatives you've considered

• Right now you can create a dummy event using $set to create an event with these properties.
• This does make the property appear in the dropdown.
• But this can also cause a bit of extra data baggage that isn't needed, such as updating random person properties or creating a dummy user.

Additional context

• From https://us.posthog.com/project/2/support/tickets/66749

Debug info

- [X ] PostHog Cloud, region and project ID: [please provide, you can find both at https://app.posthog.com/settings/project-details#variables]
- [ ] PostHog Hobby self-hosted with `docker compose`, version/commit: [please provide]
- [ ] PostHog self-hosted with Kubernetes (deprecated, see [`Sunsetting Kubernetes support`](https://posthog.com/blog/sunsetting-helm-support-posthog)), version/commit: [please provide]

Start with the feature flag matching-rules flow and the setPersonPropertiesForFlags and setPersonProperties behavior described in the issue; trace how properties become available in the matching-criteria selector. Done means these ephemeral properties can populate selectable criteria without requiring a dummy event, with regression coverage for the new behavior.