## Motivation
The motivation of this PR is to add `gt_edge_map` field to support
boundary loss.
## Modification
- GenerateEdge
Modify `gt_edge` field to `gt_edge_map`.
- PackSegInputs
Add `gt_edge_map` to data_sample.
- stack_batch
Pad `gt_edge_map` to max_shape.
## BC-breaking (Optional)
No
## Use cases (Optional)
Reference `GenerateEdge`.