Layer/Modal background overlay - Phase 1 Build

[SeamusLeonardHPE]

Currently Grommet applies a background overlay for Layer component when the prop modal={true} is applied.

Currently we do not have this as a prop on the layer component set (center/side-drawer/fullscreen in figma - Nor do we have a BG frame component with the tokenized BG color that would allow a product design to compose this.

For a build and management perspective in figma its easier to have a separate component to manage BG.

• Create a frame component to accompany the other layer components