Deconz-rest-plugin: Schedule time cannot be randomized

Feature request type

When creating a schedule using the REST API the time cannot be randomized.

Description

Send a POST request to /api/<username>/schedules with the following body:

{
    "name": "SOn_28_Schedule 1_JbUwF",
    "description": "28",
    "localtime": "2020-07-20T19:30:00A00:10:00",
    "time": "2020-07-20T19:30:00A00:10:00",
    "command": {
        "address": "/api/<username>/groups/28/scenes/4/recall",
        "method": "PUT",
        "body": {}
    },
    "status": "enabled",
    "autodelete": false,
    "recycle": false
}

The request should be successful. However, the random part of the (local)time (A00:10:00) is ignored. That can be seen in the source code here:

https://github.com/dresden-elektronik/deconz-rest-plugin/blob/4154ad416996058bda9ab2d1af622fe5bef45cec/rest_schedules.cpp#L417-L425
https://github.com/dresden-elektronik/deconz-rest-plugin/blob/4154ad416996058bda9ab2d1af622fe5bef45cec/rest_schedules.cpp#L833-L841

Additional context

The Hue API supports randomized schedules.
The issue was originally reported here: https://community.hueessentials.com/t/randomize-schedule-and-phoscon-bridge/243