[send.key] Update send.key when account encryption key is rotated (#1417)

* Rotate send.key with account encryption key

* Update tests

* Improve and refactor style, fix typo

* Use null instead of empty lists

* Revert "Use null instead of empty lists"

This reverts commit 775a52ca56.

* Fix style (use AddRange instead of reassignment)

src/Core/Models/Api/Request/Accounts/UpdateKeyRequestModel.cs

@@ -12,6 +12,7 @@ namespace Bit.Core.Models.Api
         public IEnumerable<CipherWithIdRequestModel> Ciphers { get; set; }
         [Required]
         public IEnumerable<FolderWithIdRequestModel> Folders { get; set; }
+        public IEnumerable<SendWithIdRequestModel> Sends { get; set; }
         [Required]
         public string PrivateKey { get; set; }
         [Required]

src/Core/Models/Api/Request/SendRequestModel.cs

@@ -130,4 +130,10 @@ namespace Bit.Core.Models.Api
             return existingSend;
         }
     }
+
+    public class SendWithIdRequestModel : SendRequestModel
+    {
+        [Required]
+        public Guid? Id { get; set; }
+    }
 }