Fix intermittent CI/CD analytics request error for 180 day windows

What does this MR do and why?

We were seeing occasional errors on the CI/CD analytics page when using the Last 180 days time period.

This was happening because the REST API was using the time period start_date.at_beginning_of_day -> Time.current.at_end_of_day, as opposed to the GraphQL API which was using start_date.at_beginning_of_day -> Time.current.at_beginning_of_day. That small difference was enough to increase the time window to be slightly larger than what is allowed, causing the request to fail.

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Before	After

How to set up and validate locally

1. Visit CI/CD analytics page for any group (ex. http://gdk.test/groups/flightjs/-/analytics/ci_cd?tab=deployment-frequency)
2. Click the Last 180 days tab
3. Check for a page alert indicating the error

MR acceptance checklist

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

Related to #412356 (closed)