Release 2138

Trello card

https://trello.com/c/aV8OpoWy

Context

Placement requests for flex dates are expired the next day after they are created, which is confusing for the school managers.

We want to mark them as expired when they are archived (2 months after they are received).

Changes proposed in this pull request

Update the placement request #flex_date_expired? to return true after two months of the created_at date.

Guidance to review