[PM-27123] Account Credit not Showing for Premium Upgrade Payment (#6484)

* feat(billing): add PaymentMethod union

* feat(billing):  add nontokenized payment method

* feat(billing): add validation for tokinized and nontokenized payments

* feat(billing): update and add payment method requests

* feat(billing): update command with new union object

* test(billing): add tests for account credit for user.

* feat(billing): update premium cloud hosted subscription request

* fix(billing): dotnet format

* tests(billing): include payment method tests

* fix(billing): clean up tests and converter method

src/Core/Billing/Payment/Models/PaymentMethod.cs

@@ -0,0 +1,69 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using OneOf;
+
+namespace Bit.Core.Billing.Payment.Models;
+
+[JsonConverter(typeof(PaymentMethodJsonConverter))]
+public class PaymentMethod(OneOf<TokenizedPaymentMethod, NonTokenizedPaymentMethod> input)
+    : OneOfBase<TokenizedPaymentMethod, NonTokenizedPaymentMethod>(input)
+{
+    public static implicit operator PaymentMethod(TokenizedPaymentMethod tokenized) => new(tokenized);
+    public static implicit operator PaymentMethod(NonTokenizedPaymentMethod nonTokenized) => new(nonTokenized);
+    public bool IsTokenized => IsT0;
+    public bool IsNonTokenized => IsT1;
+}
+
+internal class PaymentMethodJsonConverter : JsonConverter<PaymentMethod>
+{
+    public override PaymentMethod Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        var element = JsonElement.ParseValue(ref reader);
+
+        if (!element.TryGetProperty("type", out var typeProperty))
+        {
+            throw new JsonException("PaymentMethod requires a 'type' property");
+        }
+
+        var type = typeProperty.GetString();
+
+
+        if (Enum.TryParse<TokenizablePaymentMethodType>(type, true, out var tokenizedType) &&
+            Enum.IsDefined(typeof(TokenizablePaymentMethodType), tokenizedType))
+        {
+            var token = element.TryGetProperty("token", out var tokenProperty) ? tokenProperty.GetString() : null;
+            if (string.IsNullOrEmpty(token))
+            {
+                throw new JsonException("TokenizedPaymentMethod requires a 'token' property");
+            }
+
+            return new TokenizedPaymentMethod { Type = tokenizedType, Token = token };
+        }
+
+        if (Enum.TryParse<NonTokenizablePaymentMethodType>(type, true, out var nonTokenizedType) &&
+            Enum.IsDefined(typeof(NonTokenizablePaymentMethodType), nonTokenizedType))
+        {
+            return new NonTokenizedPaymentMethod { Type = nonTokenizedType };
+        }
+
+        throw new JsonException($"Unknown payment method type: {type}");
+    }
+
+    public override void Write(Utf8JsonWriter writer, PaymentMethod value, JsonSerializerOptions options)
+    {
+        writer.WriteStartObject();
+
+        value.Switch(
+            tokenized =>
+            {
+                writer.WriteString("type",
+                    tokenized.Type.ToString().ToLowerInvariant()
+                );
+                writer.WriteString("token", tokenized.Token);
+            },
+            nonTokenized => { writer.WriteString("type", nonTokenized.Type.ToString().ToLowerInvariant()); }
+        );
+
+        writer.WriteEndObject();
+    }
+}