fix(parameter-based): respect [EnumMember] attribute when serialising enum query parameters

ParameterBased.getParameters() was calling .ToString() on enum values, producing
the C# identifier name (e.g. FINANCIALEVENTGROUPID) rather than the wire format
declared in [EnumMember(Value = "...")] (e.g. FINANCIAL_EVENT_GROUP_ID). This
caused every enum-typed query parameter to be silently rejected by Amazon APIs.

Fix: use StringEnumConverter (Newtonsoft.Json) for both the scalar enum and the
IEnumerable<TEnum> branches so [EnumMember] attribute values are honoured.

Also: type relatedIdentifierName on ParameterListFinancialTransactions20240619 as
RelatedIdentifierNameEnum? instead of string? now that the serialisation is correct.

Author: ProNotion

Source/FikaAmazonAPI/Parameter/Finance/ParameterListFinancialTransactions20240619.cs

@@ -19,10 +19,10 @@ public class ParameterListFinancialTransactions20240619 : ParameterBased
         /// </summary>
         public string? transactionStatus { get; set; }
         /// <summary>
-        /// Possible values:`FINANCIAL_EVENT_GROUP_ID`: the financial event group ID associated with the transaction.
-        ///*Note: FINANCIAL_EVENT_GROUP_ID is the only `relatedIdentifier` with filtering capabilities at the moment. While other `relatedIdentifier` values will be included in the response when available, they cannot be used for filtering purposes.
+        /// The identifier name to filter by. Only FINANCIAL_EVENT_GROUP_ID has filtering capability at the moment;
+        /// other values appear in response payloads but cannot be used as query filters.
         /// </summary>
-        public string? relatedIdentifierName { get; set; }
+        public RelatedIdentifierNameEnum? relatedIdentifierName { get; set; }
         public string? relatedIdentifierValue { get; set; }
         public string nextToken { get; set; }
         public int? MaxNumberOfPages { get; set; }

Source/FikaAmazonAPI/Parameter/ParameterBased.cs

@@ -57,11 +57,22 @@ public virtual List<KeyValuePair<string, string>> getParameters()
                     }
                     else if (p.PropertyType.IsEnum || IsNullableEnum(p.PropertyType))
                     {
-                        output = value.ToString();
+                        var enumSettings = new JsonSerializerSettings
+                        {
+                            Converters = new List<JsonConverter> { new StringEnumConverter() }
+                        };
+                        output = JsonConvert.SerializeObject(value, enumSettings).Trim('"');
                     }
                     else if (IsEnumerableOfEnum(p.PropertyType) || IsEnumerable(p.PropertyType))
                     {
-                        var data = ((ICollection)value).Cast<object>().Select(a => a.ToString());
+                        var enumSettings = new JsonSerializerSettings
+                        {
+                            Converters = new List<JsonConverter> { new StringEnumConverter() }
+                        };
+                        var data = ((ICollection)value).Cast<object>()
+                            .Select(a => a.GetType().IsEnum
+                                ? JsonConvert.SerializeObject(a, enumSettings).Trim('"')
+                                : a.ToString());
                         if (data.Count() > 0)
                         {
                             var result = data.ToArray();