Make default_max_count query uses expires_at

What does this MR do?

Make default_max_count query uses expires_at instead of current time, when timestamp is not provided.

When timestamp is not provided, historical_data would use current time, while default_max_count would use license expires_at (see https://gitlab.com/gitlab-org/gitlab/-/blob/3f139e5d0925b5287d07bdd0dcbc26c98c8caeff/ee/app/models/license.rb#L694)

This commit fix default_max_count to align with historical_data

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Related to #326931