Precise rolling interval

[Parsa2820]

We need to specify rolling interval more accurate than just Minute, Hour, Day, Month, Year, and Infinite. How about adding a new parameter besides current RollingInterval enum parameter, for example string preciseRollingInterval which can get values like "2h 30m 4s"?

This is the orginal comment on a PR : #182 (comment)

[tkrafael]

I've added more intervals into serilog.
#204

I think there must be a cleaner way to add custom interval besides enum values.

[bartelink]

Realistically the current high level approach of defining rolling intervals is not something that's viable to change given the broad use of this sink

Closing as a duplicate of #243, #225 and/or #298 - the most viable way for anything to change is to have a fork demonstrate something that works, take the learnings from that, map it to a feature request here, and have someone implement it