Implement our masterplan about fallback DNS round-robin pool & HTTPS
_Originally created by @Anonymous on [#12833 (Redmine)](https://public-redmine-archive.tails.boum.org/code/issues/12833)_
see <https://labs.riseup.net/code/issues/9796#note-25>
Blueprint: https://tails.boum.org/blueprint/HTTP_mirror_pool/#HTTPS
Feature Branch: 451f/mirror-pool-dispatcher.git/master and 451f:tails.git/feature/12833+use_wikimedia_mirror
### Related issues
- **Related to** tails/tails#9796
- [ ] **Blocked by** tails/tails#15908
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