Added Session and User count measurements to Visualization Designer

What does this MR do and why?

New features for the Analytics Visualization Designer

• Adds the posibility to measure sessions, sessions duration, sessions repeat percentage and session avg count
• Adds the posibility to measure unique users
• Fixes the selection of click and feature usage events

Screenshots or screen recordings

How to set up and validate locally

1. Make sure you are on GitLab Ultimate
2. You need to set up the Product Analytics DevKit if you haven't already done so. And follow the instructions on Connecting GDK to your devkit.
3. Access /-/product_analytics/dashboards/widget-designer on an product analytics activated project like [GDK_HOST]/gitlab-org/gitlab-shell/-/product_analytics/dashboards/panel-designer.

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.

closes #384464 (closed), #385596 (closed)