xF1 Add-on Spam trigger prune config 1.0.2a

Makes the spam log prune duration configurable. Default is 30 days to match XF's defaults.

Focuses on permitting to keeping user registration records for much long than normal.

Used in conjunction with TPU: Detect and Block Spam Registrations which adds the spam trigger entry for an account under the "Registration tab" on the AdminCP profile for a user.