Update installation/upgrade process/tools/doc for amd64

Tails 2.x is 386, Tails 3.X will be amd64. We have install/v1/Tails/i386/stable/latest.yml. I guess that DAVE will need to start looking in install/v1/Tails/amd64/stable/latest.yml at some point, probably once 3.0 is out (and the release process will likely need to be updated), but I didn’t think of it much, so please design a plan and get it ready.

Please also check if other aspects of our installation/upgrade system need updating.

Feature Branch: feature/11962-update-install-and-upgrade-to-amd64-ikiwiki-setup

Parent Task: #11916 (closed)

Related issues

Related to #12495 (closed)
Blocks #12432 (closed)

Original created by @intrigeri on 11962 (Redmine)

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