Log user-agents for Fastly CDN logs

[Mark-Simulacrum]

Currently our CloudFront logs contain user agents, but the Fastly logs do not. We should fix that, probably by editing something around here: https://github.com/rust-lang/simpleinfra/blob/86a318bdd2ca6092a6bcc3c4f81ef541e7bd78b7/terragrunt/modules/release-distribution/fastly-static.tf#L108 to include a user agent (https://www.fastly.com/documentation/reference/api/logging/s3/)