PM-2035: PRF Unlock (#6401)

* Initial refactor

* Add WebauthnPRFOptions to syncResponse

* MAYBE: Use KM owned ResponseModel?

* REVERT ^- Keep using PrfUnlockOptions for simplicity

This reverts commit 5a34e7dfa8.

* UserDecryptionOptions: Only send one credential

* format

* Update UserDecryptionOptions.cs

* format

* Added feature flag (#6600)

src/Core/KeyManagement/Models/Api/Response/UserDecryptionResponseModel.cs

@@ -1,4 +1,7 @@
-namespace Bit.Core.KeyManagement.Models.Api.Response;
+using System.Text.Json.Serialization;
+using Bit.Core.Auth.Models.Api.Response;
+
+namespace Bit.Core.KeyManagement.Models.Api.Response;
 
 public class UserDecryptionResponseModel
 {
@@ -6,4 +9,10 @@ public class UserDecryptionResponseModel
     /// Returns the unlock data when the user has a master password that can be used to decrypt their vault.
     /// </summary>
     public MasterPasswordUnlockResponseModel? MasterPasswordUnlock { get; set; }
+
+    /// <summary>
+    /// Gets or sets the WebAuthn PRF decryption keys.
+    /// </summary>
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public WebAuthnPrfDecryptionOption[]? WebAuthnPrfOptions { get; set; }
 }