Add Keep After Archive for Tasks

[mfeit-internet2]

For 5.0.0, a new task parameter called keep-after-archive has been added that governs how long runs are kept after the last archiving is complete. (See pscheduler/#1071.).)

The value is an ISO 8601 duration. If not set, the parameter should not be present in the generated task specification.

The task's schema must be set to at least 5 if this parameter is present.

Per discussion: Add this to each test entry in config section.

Sample JSON:

{
    "schema": 5,  <----- NEW
    "archives": [
        ...
    ],
    "keep-after-archive": "PT30S",    <----- NEW
    "test": {
        ...
    }
}

[grigutis]

0f4f35fe600dafb82d45d30cf731a3ca74d44c35 resolves this issue.