WIP: Resolve "Avatars make blame page slow"

What does this MR do?

Fetches avatar icons on the blame page with a single query rather than a query for each commit.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Improves blame page performance, esp with large numbers of commits.

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?

Closes #27345 (moved)

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