[UX] It should be possible to set retry duration to off (similar to idle duration and max duration) for unlimited duration

[peterschmidt85]

Problem:

Sometimes, I want the retry duration to be infinite, e.g. until I interrupt the command, or forever in case it's a service.

Currently, if I don't set duration, it's set to 1h automatically. This is not convenient at all.

Solution:

1. (Major) Allow to set duration to off
2. (Minor) Document the default duration