scheduled_task: SPIKE - Determine if minutes_interval / minutes_duration should support ISO8601 strings in addition to numeric values

The current trigger hash accepts a numeric value for minutes_interval and minutes_duration because of how values are specific in the V1 scheduled task API.

However, in the V2 API those values are actually specified as ISO8601 duration strings which are string values formatted like PnYnMnDTnHnMnS. These strings are much more complex, but are also much more expressive / easy to read when the times get beyond 60 minutes.

See duration values as specified in this gist:
https://gist.github.com/Iristyle/58ff446bd3f60e68d52df3868c917a0e#itrigger

Determine if the Repetition values in the hash minutes_interval and minutes_duration should allow this format string in addition or in place of a numeric minutes. These string formats will need to be accepted for other aspects of the trigger (such as ExecutionTimeLimit, RandomDelay and Delay (MODULES-7215)) anyhow, so it may be worth supporting the newer format, with a fallback to a numeric-only value meaning minutes.