Fix snowplow events over time visualization show the page view count

What does this MR do and why?

This updates events over time visualization to show the events count instead of incorrectly showing the page view count.

A related issue for total events will be fixed in Fix Total Events visualization showing incorrec... (!122278 - merged).

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Follow these instructions to set up Product Analytics in your GDK. Make sure you're devkit has the latest main branch changes.
2. Enable the Snowplow flag by running the command: echo "Feature.enable(:product_analytics_snowplow_support)" | rails c.
3. Set up a new project and onboard it with Snowplow via Project → Analytics → Dashboards.
4. Track some events and page views for the project via the SDK.
5. Visit the Behaviour dashboard at Project → Analytics → Dashboards -> Behavior and verify panels display correct data.

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.

Related to #414595 (closed)