add grubalt bootchooser

[mbessler]

The grubalt bootchooser is an alternative Grub-based bootchooser that works more like the uboot bootchoser.

The grubalt bootchooser requires Grub built with decrement support. Currently this feature requires patching Grub: https://src.fedoraproject.org/rpms/grub2/blob/db4a99687c8306760702abda9c01a2e74d19a3f3/f/0253-Reimplement-boot_counter.patch

[jluebbe]

Rebased to master to retrigger CI.

[jluebbe]

The code looks looks good, although I'd prefer something like "grub-counting" as the name, as "alt" is too generic.

Before merging this, we'd prefer having the corresponding support upstream in grub. @mbessler, are you aware of attempts to get this merged? I've not found any in a quick search.

We can leave this PR open so anyone can use it together with the grub patch, of course.

[mbessler]

The code looks looks good, although I'd prefer something like "grub-counting" as the name, as "alt" is too generic.

Sounds like a better name choice than mine :) I'll see when I can update the names and push an update.

Before merging this, we'd prefer having the corresponding support upstream in grub. @mbessler, are you aware of attempts to get this merged? I've not found any in a quick search.

I've not tried engaging with the Grub team. If someone else wants to try, please do.

We can leave this PR open so anyone can use it together with the grub patch, of course.

How about carrying the patch in meta-rauc until upstream Grub integrates it (if ever)?

[ejoerns]

@mbessler We could have both patch sets in meta-rauc, yes. This would at least ensure that we have a consistent environment.
However, at the moment I am not yet very convinced that this is a better option than finding someone who has an interest in pushing these things towards GRUB mainline, because it means additional maintenance effort for meta-rauc without knowing if it is actually used or a benefit for others.