testing/zsh-theme-powerlevel10k: rewrite aport
- Don't build gitstatus, it's packaged separately.
- Install it into our standard location for Zsh plugins (/usr/share/zsh/plugins).
- Fix file permissions - they shouldn't be executable.
- Simplify package() function.
- Add powerlevel10k.plugin.zsh for compatibility with the plugins loader in Alpine's default /etc/zsh/zshrc.