Do not log artifacts entry file retrieval

What does this MR do and why?

In the API endpoint in which we make it possible to retrieve a single entry from a ZIP artifacts archive, we should not log entire archive size, since only a single entry will be transferred to a client. Logging entire archive size is not accurate since a 1 byte file can be transferred out of 1 GB archive.

Instead, we should add instrumentation on the Workhorse side.

/cc @morefice

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