add missing string length checks

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

@@ -13,6 +13,7 @@ namespace Bit.Core.Models.Api
         public string Name { get; set; }
         [Required]
         public bool? AccessAll { get; set; }
+        [StringLength(300)]
         public string ExternalId { get; set; }
         public IEnumerable<SelectionReadOnlyRequestModel> Collections { get; set; }