[Network Slice Mngr] Add Slice Instantiation Parameters

[alemanyp]

In order to make it easy when deploying the different pilots use cases where the slice mngr is involved. This issue is to ask the modification of the json that the GTK sends to the slice-mngr when a slice instantiation request.

The current json has this structure:

{
     "nstdId": "",
     "name": "",
     "description": "",
     "callback": ""
}

The NEW structure just needs a new key to be added:

{
  "nstdId": "",
  "name": "",
  "description": "",
  "callback": "",
  "instantiation_params": [
    {
      "subnet_id": "",
      "sla_id": "",
      "sla_name": "",
      "ingresses": "",
      "egresses": "",
      "vim_id": "uuid"
    }
  ]
}

[alemanyp]

It is not a required field like the 4 that are already sent.