Build a list of fast and reliable HTTP mirrors

We need a few ones (3-5) to be put in a DNS round-robin pool that will serve as a fallback for downloads when JavaScript is disabled when visiting the download page on our website.

Blueprint: https://tails.boum.org/blueprint/HTTP_mirror_pool/#speed

Parent Task: #7161 (closed)

Related issues

Has duplicate #11283 (closed)
Blocks #11284 (closed)

Original created by @intrigeri on 10295 (Redmine)

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