[Feature request]: Allow atuin dotfiles alias to be OS platform specific

[mattzago]

I really like the idea of atuin dotfiles alias, but I find it's very common to use shell functions with operating system detection to set different alias values.

For example on macOS for ls one might set ll=ls -laG but on Linux they may use ll=ls -la --color=auto for the equivalent because of the difference between GNU ls and macOS ls color arguments.

I can work around this with different alias names, but it would be useful to have alias values be conditional depending on the detected operating system atuin is running on.