Fix timerange bug with Event Stats query

[alyssabull]

There was a bug that was not setting the timezone and causing data to:

• Not accurately reflect a chosen timezone (i.e. displaying UTC time instead of local time)
• Not accurately display a given time range (i.e. when last 24 hours is chosen, there would be missing data)

The timezone is now added to the params so the data will properly display.

[github-actions]

Use the following command to run this PR with Docker at http://localhost:3000:

docker run --rm -p 3000:3000 grafana/plugin-builds:029b871c92a5cfc988630c23628f3ef37d6dd818pre