[ENHANCEMENT] Vertical panel alignment options

[athyfr]

I think vertical alignment options would make things more intuitive.

This would mean you could:

programs.plasma.panels.example = {
  location = "left";
  alignment = "down"; # Could also be "center" or "up".
};

It probably doesn't need any real new implementation, just some kind of alias.

I'm relatively new to NixOS so forgive my ignorance. I would submit a PR myself if I new how to use Git/GitHub. I need to learn that still..