Proposal: use TD `default` values

hello,
I'd like to propose the scripting API to define variables the consumer leaves undefined with the default values from the TD (or const values?).

A simple use-case would be a Thing, expecting a fixed payload parameter based on the Interaction Affordance, like in the TD below.

Now with the scripting API using the default values a user won't have to worry about knowing the correct commandId.

{
  "actions": {
    "move": {
      "type": "object",
      "properties": {
        "commandId": {
          "type": "integer",
          "default": 5
        },
        // other dynamic properties like coordinates
      }
    },
    "dimLight": {
      "type": "object",
      "properties": {
        "commandId": {
          "type": "integer",
          "default": 6
        }
        // other dynamic properties like time span
      }
    }
  }
}

Start by locating the scripting API path that builds action payloads from a Thing Description, then determine how omitted variables and TD default or const values should be handled. Done should include a decided behavior for the commandId example and tests covering omitted values; the issue names no files or tests.