[Usage quotas] Usage progress bar is not using design tokens

Background

This issue represents a finding from our work to audit features belonging to ~"group::personal productivity. See Designer audit of Personal Productivity features (#519378 - closed) for more information.

Problem to solve

• Usage progress bar is not using design tokens
• This will prevent the Group Settings / Usage Quota / Pages page from adapting properly to dark mode.

Proposal

• The problem stems from https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/usage_quotas/components/sectioned_percentage_bar.vue#L34
• Using colorFromDefaultPalette is appropriate here for light mode, but we need to update it to use colorFromDarkPalette when the app is in dark mode.
• JS constant colors initialised in charts will always return hotpink findings with our current tooling, in that sense they may be false positives if we want constant colors between color modes for data visualisation colors.

Screenshots