[PM-25982] Restrict Ciphers being assigned to Default from Shared collections (#6382)

* validate that any change in collection does not allow only shared ciphers to migrate to a default cipher

* refactor order of checks to avoid any unnecessary calls

* remove unneeded conditional

src/Api/Vault/Controllers/CiphersController.cs

@@ -887,6 +887,9 @@ public class CiphersController : Controller
     [HttpPost("bulk-collections")]
     public async Task PostBulkCollections([FromBody] CipherBulkUpdateCollectionsRequestModel model)
     {
+        var userId = _userService.GetProperUserId(User).Value;
+        await _cipherService.ValidateBulkCollectionAssignmentAsync(model.CollectionIds, model.CipherIds, userId);
+
         if (!await CanModifyCipherCollectionsAsync(model.OrganizationId, model.CipherIds) ||
             !await CanEditItemsInCollections(model.OrganizationId, model.CollectionIds))
         {