UI: Add support for dark mode

[ddeath]

Checklist

• I've searched the issue queue to verify this is not a duplicate feature request.
• I've pasted the output of kargo version, if applicable.
• I've pasted logs, if applicable.

Proposed Feature

It would be nice to support Dark mode. If this is something you would like to have, I can help with it as well.

Motivation

I am developer and I like to live in a cave :D and Kargo is too bright for that. Some browser extensions can do the job but would be nice to have dark mode native support.

Suggested Implementation

antd supports theming so this should not be too difficult to do. However we are missing "User settings" but I saw somewhere in other issue that you want to have User info section similar to ArgoCD so eventually it could sit there

[krancour]

I like dark mode as well and at some point in the past we had it, or had at least experimented with it. @rbreeze had reported that it was proving to onerous to ensure that every change looked good in both modes and we committed to just light.

I'm open to that decision being re-evaluated by @Marvin9 and defer to his judgement, but if we do it, this is going to be a low-priority enhancement.

[ddeath]

Not perfect but kind of working 1 liner dark mode is this css:

body {
  filter: invert(88%) hue-rotate(180deg);
}