Change default zsh prompt from Starship to powerlevel10k

[amogus07]

I know it has limited support, but so far there's only one problem I've noticed when using it related to an optional feature. It's considerably faster and provides better integration with zsh (e. g. instant prompt) since powerlevel10k itself is written in zsh (except for gitststatus). I've used Starship before, but I switched to powerlevel10k because of it's better performance thanks to instant prompt.

[amogus07]

Also, the documentation doesn't seem to make it clear wether starship is included in the non-dx image. If it isn't you could probably add the dx label as well. I'll probably create an issue or a pr about that on the documentation repo.