feat(json-api-context): add total records prop

Author: jaredcnance

src/JsonApiDotNetCore/Services/JsonApiContext.cs

@@ -20,13 +20,15 @@ public JsonApiContext(
             _httpContextAccessor = httpContextAccessor;
             Options = options;
         }
+
         public JsonApiOptions Options { get; set; }
         public IContextGraph ContextGraph { get; set; }
         public ContextEntity RequestEntity { get; set; }
         public string BasePath { get; set; }
         public QuerySet QuerySet { get; set; }
         public bool IsRelationshipData { get; set; }
         public List<string> IncludedRelationships { get; set; }
+        public int TotalRecords { get; set; }
 
         public IJsonApiContext ApplyContext<T>()
         {