Task archival

[pablito-perez]

As a µTask operator, I'd like to limit the amount of finished tasks that are left in my "live" table: this could hit the performance of the engine when collecting unfinished tasks.

The task expiration parameter in µTask's configuration allows me to set a period after which they get deleted

However, I'd still like to keep a trace of those tasks, for auditing purposes, and it is practical for me that they remain within µTask, to leverage its security guarantees

Hence, an option to "archive" finished tasks instead of outright deleting them would be valuable

Design TBD (a copy of the task and resolution tables? a new set of API endpoints to retrieve this data?)