Drop external_image_sbom.sbom column

[divolgin]

No description provided.

[greptile-apps]

Greptile Summary

Removes the legacy external_image_sbom.sbom text column now that SBOM payloads are stored and read from object storage.

• Updates the SchemaHero table definition so future schema applications drop the obsolete PostgreSQL payload column.
• Retains the digest/architecture key, metadata, and object-store migration flag.

Confidence Score: 5/5

The PR appears safe to merge because current SBOM persistence and retrieval no longer depend on the removed database column.

The schema change removes only the legacy payload column while preserving all metadata and object-store fields used by current application paths.

Important Files Changed

Filename	Overview
db/schema/tables/external-image-sbom.yaml	Removes the legacy database SBOM payload column consistently with the existing object-storage-only write and read paths.

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