Optionally fail for slow tests

In a number of projects we are adding in CI that will fail unit tests if they take longer than X e.g.
* https://github.com/bluesky/ophyd-async/issues/729
* https://github.com/DiamondLightSource/dodal/issues/1003
* https://github.com/DiamondLightSource/mx-bluesky/issues/663

Given this is used by lots of different repos we should put it in the template for people to use optionally.

Start by locating the template's CI and test configuration, then compare the linked projects' slow-test handling. Done means generated projects can optionally enable a configurable failure threshold for slow unit tests without affecting projects that leave the option disabled.

Scritto dal modello di indicizzazione a partire dal testo della issue.