[FTS+SDK] Search Request to now include a "collections" setting

SDK will now need to support a new "collections" setting within an FTS search request.

The "collections" attribute within the search request will need to accept an array of strings.

Here's an example ..

{

  "from": 0,

  "size": 10,

  "query": {

    "term": "text",

    "field": "fieldName"

  },

  "collections": [

    "collection1",

    "collection2"

  ]

}