Add new parameter to "themeQuartz"

[arthurchtdSpark]

Hello !

Currently, it's possible to customize the color of checkboxes in the Grid, which is great. However, it would be very useful to have a way to configure the color of selection borders, focus outlines, and other related UI highlights in a unified way.

AG Grid already supports this with a the parameter "accentColor" (https://www.ag-grid.com/javascript-data-grid/theming-parameters/) in theme configuration, which makes it easy to apply consistent styling to interactive elements such as checkboxes, radio buttons, and focus rings.

Proposal:
Add support for a single configuration option (e.g., Emphasis color) at the "Styles" section, which applies to:

• Checkbox selection color
• Shadow when selection
• Focus outlines on interactive elements
• Any other accent/highlight elements in the grid

Benefits:

• Maintains visual consistency across all UI components inside the grid
• Simplifies theming and customization (fewer parameters to fill in)
• Improves accessibility by making selected states more visible and coherent with the brand or app color palette

I've implemented it on a custom component but thought it might be nice to share the info with you :) (here's a video showing it: loom)

Thanks!