Change metric SQL queries calls to be deterministic

What does this MR do and why?

Related to #347545 (closed).

This changes the Gitlab::Usage::ServicePingReport calls for metric SQL queries return the same results between calls (barring timestamps) to make future iterations on #347545 (closed) easier.

Previously, some metric values would differ between calls (for example, raw Proc objects with different stringified object ids).

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