Convenient creation of parent objects for modify commands with nested JSON paths

[thjaeckle]

As part of #696, but also as a general useful enhancement of Ditto, it shall be supported to create/modify nested JSON fields inside a thing without the need that their parents in the JSON are create before.

Currently, when you have the following thing JSON (which you can do, this is valid):

{
  "thingId": "org.eclipse.ditto:my-thermostat-1",
  "policyId": "org.eclipse.ditto:my-thermostat-1",
  "features": {
    "Thermostat": {
      "definition": [ "org.eclipse.ditto:Thermostat:1.0.0" ]
    }
  }
}

it is not possible to "just" create the "on" property with the following HTTP PUT request:

PUT /api/2/things/org.eclipse.ditto:my-thermostat-1/features/Thermostat/properties/on
true

Up to now, you would get a HTTP error 404 (not found) as the properties object was not yet created.

This shall be simplified by automatically creating missing JSON objects, which also the desired properties API will benefit from.
There, when you want to create one single desired property, you would just have to make an HTTP call:

PUT /api/2/things/org.eclipse.ditto:my-thermostat-1/features/Thermostat/desired/configuration/target-temperature
22.0

This API call will be accepted and the thing JSON will look like:

{
  "thingId": "org.eclipse.ditto:my-thermostat-1",
  "policyId": "org.eclipse.ditto:my-thermostat-1",
  "features": {
    "Thermostat": {
      "definition": [ "org.eclipse.ditto:Thermostat:1.0.0" ],
      "desired": {
        "configuration": {
          "target-temperature": 22.0
        }
      }
    }
  }
}

[thjaeckle]

When using the merge thing done in #950 the implicit convenient creation of parent objects already exists.

So we might also close this issue.