Ecto schema for durable source ingestion records.
Uses a composite primary key of (tenant_id, repo_id, source_id). This schema is engine-agnostic.
(tenant_id, repo_id, source_id)
@type t() :: %MnemosyneEcto.Schema.Ingestion{ __meta__: term(), fingerprint_version: term(), node_ids: term(), payload_digest: term(), repo_id: term(), source_id: term(), stored_at: term(), tenant_id: term() }