Draft a "user" (aka. RM) story for the reproducible release process

Let’s draft a user story for the RM. Here are some notes:

once I have built my own release .iso, instead of uploading it I just generate the .sig and send it to Jenkins somehow. if it managed to build an .iso that that .sig can verify, then it will publish the ISO itself
this ensures that we never release something that hasn’t been reproduced once, and makes bandwidth less important for RMs

Parent Task: #5630 (closed)

Related issues

Is duplicate of #12629 (closed)

Original created by @u on 12628 (Redmine)

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