Dark mode: rework Color Modes pages

[julien-deramond]

Description

This PR revamps the Color Modes page by taking into account some remaining sub-tasks from #2223:

Boosted documentation to explain this concept in the color modes page (dark variant vs dark mode) or maybe just in the migration guide? + link in all dark variant components to this section

Color modes: _color-modes.md should explain in detail the impact and the usage of data-bs-theme (color, background-color, contextual, container contextual vs component contextual, the difference with dark variant, etc.)

• When applied on a component directly, weird behavior can happen (see Auto color and bg-color with data-bs-theme #2313); especially with the basic HTML elements, form controls, etc.

Live previews

• https://deploy-preview-2442--boosted.netlify.app/docs/5.3/customize/color-modes#dark-mode

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