Stop storing attestations in database when CAS backend is configured

[migmartri]

Summary

Currently, when an attestation is pushed, it is always stored in a database table regardless of whether a Content Addressable Storage (CAS) backend is configured. This is redundant and increases database size unnecessarily.

Proposal

Change the attestation storage behavior so that:

• When a CAS backend is configured: Store the attestation only in the CAS. Do not persist it in the database table.
• When no CAS backend is configured: Continue storing the attestation in the database as a fallback.

This will reduce database storage requirements and avoid duplication of attestation data for organizations that have a CAS backend set up.