[Blocks] - Add breadcrumb to variant-editing experience to show the main block

## Current behavior
The block header shows the variant name, without referencing the main block

## Proposed change
Add breadcrumb above the variant name

## Design
https://www.figma.com/design/qmXP7Fd0SCg8FXu4GTuSFp/DISCO-%7C%7C-Design-System-v1.1?node-id=14758-6503&t=OmGxWVB4KHbdR3dT-1

## Additional notes
Add any other context about the feature request here.
