Add default expiration configuration at definition and global levels

Description

Introduce default expiration configuration at the definition and global levels using period-based logic. This supplements the existing issue-level expiration, which remains as a per-approval parameter allowing exact date settings.


Accepted criteria

  • Supports setting default expiration at the global level using period-based values

  • Supports setting default expiration at the definition level using period-based values

  • Issue-level expiration remains unchanged and allows setting exact expiry dates per approval

  • Definition-level defaults override global defaults when both are present