image_types_balena.bbclass: Move image signing code here

[floion]

This fixes the following error:

cp: cannot stat '/work/build/tmp/deploy/images/generic-amd64/balena-image-generic-amd64.balenaos-img.sig': No such file or directory

The signed image symlink is not generated before the flasher needs it so we avoid this dependency issue by defining a new image type for which the build system will automatically create the appropriate symlink.

Change-type: patch

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[floion]

Hi @klutchell just a heads up that I pushed a change to this PR but that did not make it invalidate the policy-bot. Even more, I also re-requested another review from @alexgg but policy-bot is still marking the PR as approved.

[alexgg]

Still fails - needs some work

[floion]

Still fails - needs some work

It worked now but fails for an unrelated issue: https://github.com/balena-os/meta-balena/actions/runs/12808128684/job/35710334625?pr=3597

[alexgg]

@floion I have fixed the issues with this PR in #3600

@floion when you say it works now, did you test signed builds too?

[klutchell]

Hi @klutchell just a heads up that I pushed a change to this PR but that did not make it invalidate the policy-bot. Even more, I also re-requested another review from @alexgg but policy-bot is still marking the PR as approved.

@floion This is the expected behaviour, and has always been the case for PR approvals via policy-bot.

However, we did agree in the brainstorm yesterday to enable invalidate-on-push for some of our orgs (project). Would love to do so for balena-os as well as long as we are okay with the friction of having to re-approve every rebase.

[floion]

Superseded by #3600