[KeyVault] - Consider providing a type for ISO8601 durations

[maorleger]

Key Rotation at the service level has and will continue to use to ISO8601 durations. Currently we use strings to represent these; however, this can be a source of confusion and errors as developers must author them by hand.

To alleviate such issues, consider (along with your language architects) whether it makes sense to provide a structure that can convert to and from ISO8601 durations. Initial thoughts on the API (in TS):

class Duration {
  static parse(input: string): Duration
  toISOString(): string

  years?: number
  months?: number
  weeks?: number 
  hours?: number
  minutes?: number
  seconds?: number
}

Duration.parse("P3Y6M4DT12H30M5S").toISOString() => "P3Y6M4DT12H30M5S"

But of course this will change per language, and some languages might not want this in which case feel free to close the issue.

[heaths]

After discussion, we'll not be doing this for .NET in time for the next release but will consider it in the future. For now, we'll keep the property type a string.

[heaths]

There's been enough push back on this I'm closing. We can always revisit if we get enough customer demand.