Mention user-facing changes of `openshift/imagebuilder` in Buildah release notes

[vbvictor]

I wanted to track in which release of Buildah support for ${VERSION%%.*} shell syntax was added because it was working with Buildah-1.39 and didn't work with Buildah-1.33.

I tried to look for buzzwords "shell", "syntax", "%" in Release Notes but couldn't find anything.

So dug manually into Buildah sources to find out that this feature was added in https://github.com/openshift/imagebuilder/releases/tag/v1.2.12 which Buildah mentioned in 1.37 release as Vendor in github.com/openshift/imagebuilder to v1.2.14.

Since this is a user-facing feature in Buildah (opposed to internal version bumps like cobra to v1.8.1), I think it should be mentioned in the main release notes, e.g. https://buildah.io/releases/#changes-for-v1370.

But still thank you a lot for shell syntax support.

[github-actions[bot]]

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