Update default block image to have a hover state

[natdink]

Let's update the default block image to have a purple hover state.

Then, could you explore a visual option that could be added to indicate "no image" or something that feels like a placeholder - it shouldn't conflict with our current block images.

If no good alternatives, we can move forward with the gray box!

[sayalibhagat-Kanini]

I have designed the Default Block for hover state and created another variation for both active and hover state.

[bfekadu21]

@sayalibhagat-Kanini @natdink Keeping the gray box since there are no alternatives. Figma link for reference: https://www.figma.com/design/Qj4tWPsniFOJ6qSLfxOaBT/Drag-And-Drop---Design?node-id=9654-60158&t=VcbIw9JH56u0jYRm-4