Event tracking for require_verification_for_group_creation experiment

What does this MR do and why?

Part of https://gitlab.com/gitlab-org/growth/team-tasks/-/issues/533/

This MR adds event tracking implementation for Experiment: Require verification before create group .

It adds a call to experiment(:require_verification_for_group_creation, user: current_user).track(:converted, namespace: group) when a top-level group is created by a user. This call fires a Snowplow event with the required data needed our PMs and Data Team to analyze the outcome of the experiment.

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.