Expiration of "action" states

[peacekeeper]

Using an "action" state, the registrar can ask a client to perform some action (e.g. sign a payload, send coins, agree to a legal text, etc.). Should this state contain an expiration time after which it is not valid anymore? This could be part of didRegistrationMetadata.

Example:

{
    "jobId": "1234",
    "didState": {
      "state": "action",
      "action": "signPayload",
      "signingRequest": {
        "signingRequest1": {
          ...
        }
      }
    },
    "didRegistrationMetadata": {
        "stateExpires": "1541499210"
    },
    "didDocumentMetadata": { }
}