Support dynamic form values from an external source.

[AndreasSobczyk]

Example on JSON config file:

{
  "Runbooks": [
    {
      "RunbookName": "new-hest",
      "parameters": [
        {
          "name": "subscriptionName",
          "type": "function",
          "uri": "https://hest.test"
        },
        {
          "name": "environment",
          "type": "array",
          "array": [
            "tst",
            "dev",
            "prd"
          ]
        }
      ]
    },
    {
      "RunbookName": "new-PONY",
      "parameters": [
        {
          "name": "subscriptionName",
          "type": "function",
          "uri": "https://pony.test"
        },
        {
          "name": "environment",
          "type": "array",
          "array": [
            "tst",
            "dev",
            "prd"
          ]
        }
      ]
    }
  ]
}