place fixtures into a mirrored bucket / bake onto roachtest image

[otan]

We can occasionally get flakes with the roachtest not being able to download a resource off the internet (e.g. an ORM, prometheus).

It would be ideal if we were able to avoid this some of these by including certain elements in the image. Maybe this is just prometheus that should do this though.

Jira issue: CRDB-10086

[blathers-crl]

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[otan]

related: #51543

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