Add default_value condition definition in schema

[nmgokhale]

Here is a potential example -

{
  "default_value": {
    "parameter_ref": "updated_param",
    "value": "New default value",
    "evaluate": {
      "condition": {
        "parameter_ref": "some_param",
        "op": "isNotEmpty"
      }
    }
  }
}