grml-zsh-config: update to 0.19.18, adopt

[menaechmi]

Testing the changes

• I tested the changes in this PR: YES

Local build testing

• [x] I built this PR locally for my native architecture, (x86_64)
• I built this PR locally for these architectures (if supported. mark crossbuilds):
• [x] aarch64-musl
• [x] armv6l
• [x] i686

(it's only building docs, so as expected no issues)

zsh is also added as a dependency.

EDIT: It was pointed out I forgot to mention docs-generation changed from txt2tags to asciidoctor.

Orphaned

The maintainers last contribution to void was in December of 2019, so I am marking it orphaned. ~~I would adopt it, but I wanted to give @meator a chance as he has updated it a lot and I am less proven as a void contributor. If we get another update and no maintainer, I will do it.~~ I'll just adopt it, given an offline conversation with meator - unless any Void Maintainer disagrees.

[menaechmi]

Previous workflow failed because the email was noreply. This is fixed with the recent FP.

Also worth noting: upstream grml-etc-core is now on 0.19.19 - but the only change is removing support for runit. There's no need to update the package and then revert all of the changes. So my plan is to skip that release and patch the support back in in 0.19.20 (whenever that might be)

[menaechmi]

Resolved a merge conflict from the original being orphaned officially

[menaechmi]

I guess https://github.com/void-linux/void-packages/pull/56239 supersedes this now.