Make it possible to reproducibly generate IUKs in CI

Since we’ll generate a lot more of IUKs each release uploading them will be painful for RMs with slow internet connections.

For example, the following VM would do:

4 virtual CPUs (so the IUK generation won’t take too long)
1 GB of RAM (I used to generate IUKs in such a VM two years ago but YMMV)
10 GB /tmp for tails-iuk’s needs, and where we store the generated IUKs (before uploading them to rsync.lizard)
Access to Jenkins build artifacts

Parent Task: #15281

Original created by @anonym on 15287 (Redmine)

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