Provide form for customizable settings

Problem/Motivation

There have been several requests so far to provide customizable settings to adjust the admin interface to several desires/needs.

Proposed resolution

Provide a form with several settings to customize the UI. For example:

• - WON'T FIX, see comment #13
• Table cell padding or general spacing
• Palette
• Accent Color
• Dark mode
• Accessibility settings
  • Reduce motion
  • Highcontrast mode
  • etc.

So from this options proposed we should decide where they need to be defined and who should be able to change them:

• Settings defined across the site (per theme / per site)
• Settings defined per user (like dark mode / accessibility wise)
• Settings defined per component (like decreasing table padding or thumbnail size on Media library)

Remaining tasks

Decide per setting the following:

• In which form should it live?
• Who should be able to change it (editor/content author vs site-builder)
• Which settings/values