Add Case closed Date

[StephenOTT]

Add case closed field.

The case close date field should update when the Case State is changed to closed.

[StephenOTT]

The field can also be manually set.

[marioprudhomme]

A closed date field feels like business logic. The current date fields we are storing is modification logic (created, updated, deleted).

Would it be better to start creating an audit trail, which tracts state machine changes (and each audit would have a created date field), thus tracking the closed date that way in a more generic/clean way?