feat(api): support passing and persistenting currency code for balances

src/FiscalOS.API/Accounts/Add/Request.cs

@@ -7,6 +7,7 @@ public record Request : IValidatableObject
   public string PlaidAccountName { get; init; } = string.Empty;
   public decimal AccountCurrentBalance { get; init; }
   public decimal AccountAvailableBalance { get; init; }
+  public string AccountCurrencyCode { get; init; } = string.Empty;
 
   public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
   {
@@ -27,5 +28,11 @@ public record Request : IValidatableObject
       var fieldName = nameof(PlaidAccountName);
       yield return new($"The {fieldName} field is required.", [fieldName]);
     }
+
+    if (string.IsNullOrWhiteSpace(AccountCurrencyCode))
+    {
+      var fieldName = nameof(AccountCurrencyCode);
+      yield return new($"The {fieldName} field is required.", [fieldName]);
+    }
   }
 }