Add Color Palette Display component

[miukimiu]

EuiColorPaletteDisplay

This issue is to track the EuiColorPaletteDisplay which is a follow up on #2795 (Add Color Palette Picker component and widget).

The idea of the EuiColorPaletteDisplay is that we can use the palettes displays outside of the EuiColorPaletterPicker. So we can create this type of UIs:

Development

The color palette picker uses two functions to generate the displays inside the inputs: getLinearGradient and getFixedLinearGradient.

We can reuse these two functions to generate the palette displays. But a few things must be addressed:

• Can these two functions be converted in just one?
• Can we reuse/share code of the EuiColorStops?
• Both functions should receive stops. Right now just the getLinearGradient is able to generate a palette based on stops.