Add support for importing historical Autotask tickets into Thread so organizations can access and search ticket data created before their onboarding date. Currently, only tickets created after onboarding are visible in Thread, which creates gaps in client history and can lead to confusion, missed context, and inaccurate documentation. Users want the ability to backfill older PSA ticket history into the Thread inbox and search experience, along with clear guidance on how far back imports can go and any performance, cost, or timeline considerations associated with the process.