We need mobile equivalent of Cover block

For this first iteration, let's have these options:

• Select image from WP media library
• Use focalPoint if set on web(no settings yet, just rendering the image accordingly)
• Use overlay color if set on web (no settings yet, just rendering the color accordingly)
• Add "mimimum height in pixels" setting similar to Spacer height
• Add "background opacity" setting again similar to Spacer height using slider

Needs investigation:

Default text color to use needs some investigation. We can have a problem similar to Button block where we can't resolve the color name of that site because it uses theme colors. In that case we'll need to determine a default fallback color and use that. Same for overlay color settings.