feat(erd): show primary keys and relationship columns in generated diagram

[shubhamjrd4559-sudo]

Problem

The generated PlantUML ERD lists model fields and their types and draws relationships between tables. It does not identify primary-key columns or show which columns connect related tables. Readers must inspect the model definitions to understand key fields and join paths.

Proposed solution

Enhance the existing ERD generation data and PlantUML template to:

• Mark primary-key columns in each entity.
• Label relationships with the source and referenced columns when that metadata is available.
• Keep rendering models and relationships when optional key or column metadata is unavailable.

Context

Superset already has ERD generation tooling in scripts/erd/erd.py and a PlantUML template. The generator currently collects column names and types and renders table-level relationships. This proposal builds on that tooling to make the generated diagram more useful to developers.

Expected result

The generated ERD makes primary keys and join paths easier to understand without requiring readers to inspect each model definition.

Scope

This is a developer documentation and tooling improvement. It does not change Superset runtime behavior or database schemas.

Validation

• Add or update a focused test for the generated PlantUML output.
• Verify primary-key markers and relationship labels in the generated diagram.
• Confirm models with unavailable key or relationship-column metadata still render.

[shubhamjrd4559-sudo]

I’d be happy to work on this if the maintainers consider it a good fit. Please let me know if there are any design preferences or scope adjustments before I start.