Add flavor configuration based on the offering

[daniel-butler-irl]

• Include a custom_config picker

   {
        "key": "cluster_id",
        "type": "string",
        "default_value": "",
        "description": "The ID of the cluster to deploy the agents.",
        "display_name": "Cluster",
        "required": true,
        "custom_config": {
            "type": "cluster_var",
            "grouping": "deployment",
            "original_grouping": "deployment"
        }
    },

• ability to add options

  {
      "key": "region",
      "required": true,
      "default_value": "",
      "options": [
        {
          "displayname": "Dallas (us-south)",
          "value": "us-south"
        },
        {
          "displayname": "Frankfurt (eu-de)",
          "value": "eu-de"
        },
        {
          "displayname": "London (eu-gb)",
          "value": "eu-gb"
        },
        {
          "displayname": "Madrid (eu-es)",
          "value": "eu-es"
        },
        {
          "displayname": "Osaka (jp-osa)",
          "value": "jp-osa"
        },
        {
          "displayname": "Sao Paulo (br-sao)",
          "value": "br-sao"
        },
        {
          "displayname": "Sydney (au-syd)",
          "value": "au-syd"
        },
        {
          "displayname": "Tokyo (jp-tok)",
          "value": "jp-tok"
        },
        {
          "displayname": "Toronto (ca-tor)",
          "value": "ca-tor"
        },
        {
          "displayname": "Washington (us-east)",
          "value": "us-east"
        }
      ]
    },