docvalue_fields in Suggest response

[Treno1]

NEST/Elasticsearch.Net version:6.8.3

Elasticsearch version:6.6.2

Description of the problem including expected versus actual behavior: I`m trying to use docvalue_fields with completion suggester and I cant find FieldValues (fields in elastic responce) property in SuggestOption class.

Steps to reproduce:

1. Create index with document, containing keyword type field (or any other docvalue located field) "mem_text": { "type": "keyword", "eager_global_ordinals": true }
2. Create request via Nest with this field new SearchRequest("my_test_idx") { Suggest = new SuggestContainer(), Source = false, DocValueFields = new [] {"mem_text"} };
3. Call it with _client.SearchAsync<object>(request)
4. Check that in response in response->Suggest->Values->Options you cant find any property, which will store docvalues data (fields block in elastic response).

Proposal: Copy the following code from Hit class [JsonProperty("fields")] public FieldValues Fields { get; internal set; }

[russcam]

Closing this as #4149 has been merged and will be in the next release.