Add default date range for audit events

What does this MR do?

This MR sets default date range to this month (start of month -> today) for Audit Events. #223260 (closed)

It also sets the params[:created_before] to the end_of_day time to include events that occured on that date.

Related frontend MR to update audit events filter: !42711 (merged)

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Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

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