Identity override import

[khvn26]

Scope

• Entity resolution service function:
  • import_identity_overrides(environment, overrides_data, strategy)
    • SKIP: leave existing overrides unchanged.
    • OVERWRITE_DESTRUCTIVE: replace overrides for identities present in the data.
    • Handle edge (DynamoDB) vs non-edge projects.
• New async task: import_project_identity_overrides(project_import_id)
  • Spawned by import_project when the export contains identity_overrides and the include_identity_overrides toggle was set on the export.
  • Calls import_identity_overrides for each environment in the export.
  • Updates the ProjectImport.result_summary with identity override counts on completion.
• Enable the project_import_export_identity_overrides frontend feature flag.

Acceptance criteria (write as tests first)

• Identity overrides created for non-edge (SQL) projects.
• Identity overrides created for edge (DynamoDB) projects.
• SKIP leaves existing overrides unchanged.
• OVERWRITE_DESTRUCTIVE replaces overrides for identities present in the export.
• Task updates result_summary with identity override counts.
• Task failure does not affect the core import (steps 1-4 from the import issue remain committed).
• Export files without identity_overrides key do not spawn this task.