Adjust infrastructure and CI for USB images

Originally created by @Anonymous on #15993 (Redmine)

Adjust CI wrt. more outputs from the build jobs => more inputs for the test suite and reproducibility tests

This includes at least:
- store .img* artifacts too when building
- copy .img* artifacts too to other jobs that need them
- garbage-collect .img* too
- symlink duplicate .img* too
- Deal with increased disk space requirements on Jenkins and in the ISO archive
- probably more stuff that we’ll discover along the way
- post-release bugfixing

This work is supposed to be equally shared by groente and intrigeri.

Parent Task: tails/tails#15292

Subtasks

• #16155 (closed)
• #16157 (closed)
• #16158 (closed)
• tails/sysadmin#16159
• #16160 (closed)
• #16162 (closed)
• #16174 (closed)
• #16377 (closed)
• tails/tails#16395