Change oversized blob logging

What does this MR do and why?

• Previously, the keys of the log value were the blob.id, which is variable. The blob.id was a key in the value hash, but Kibana un-nests value hashes and returns each key in the hash as a new nested log key (with a . in the middle`).
• So JSON logging blob_detail: { 1234: abcd } from the monolith shows up as a blob_detail.1234 key in Kibana.
• Using variable key names in kibana means that each new oversized blog log line was creating a new searchable key, which clogged up our list of available keys to be an unwieldy list.
• This fixes #435117 (closed)

Screenshots or screen recordings

Bloblogs showing up in Kibana like this before (after should be blob_details.id instead)

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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