EuiToken Remove dependency on viz color palette

[ryankeairns]

An outcome of https://github.com/elastic/platform-ux-team/issues/561 , we discussed the goal of removing the tight dependency on viz colors in EuiToken (and more broadly). As it stands, the component presumes these color vars having logic built upon literal variable names.

Rough proposal
Define a new set of colors - to be used by EuiToken - that still feel part of the theme.

Notes

• Discover's field list is a very visible use case; in the initial Borealis QA some colors were deemed too light
• In the Amsterdam data viz color palette, we had 10 colors used in this component. Now, with Borealis, we picked out 5 leaving the lighter colors out (i.e. consider having 10 colors in this new palette)
• The fill version is very color rich perhaps to the point of being unusable in a UI? (see the linked issue)