Add Negative filter

Author: Milos

src/JsonApiDotNetCore/Extensions/IQueryableExtensions.cs

@@ -195,6 +195,10 @@ private static Expression GetFilterExpressionLambda(Expression left, Expression
                 case FilterOperations.like:
                     body = Expression.Call(left, "Contains", null, right);
                     break;
+                    // {model.Id != 1}
+                case FilterOperations.ne:
+                    body = Expression.NotEqual(left, right);
+                    break;
                 default:
                     throw new JsonApiException(500, $"Unknown filter operation {operation}");
             }

src/JsonApiDotNetCore/Internal/Query/FilterOperations.cs

@@ -8,6 +8,7 @@ public enum FilterOperations
         gt = 2,
         le = 3,
         ge = 4,
-        like = 5
+        like = 5,
+        ne = 6
     }
-}
+}