fix(configtree): update sentinel key when tree is imported in etcd

Wrike Task: https://www.wrike.com/open.htm?id=1459385386

riocli/configtree/etcd.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import time
 from base64 import b64encode
 from typing import Optional
 
@@ -53,6 +54,22 @@ def import_in_etcd(
             }
         })
 
+    sentinel_key = b64encode('/sentinel_key'.encode('utf-8')).decode()
+    sentinel_val = b64encode(f'{time.time_ns()}|riocli-import'.encode('utf-8')).decode()
+
+    compares.append({
+        'key': sentinel_key,
+        'result': 'EQUAL',
+        'target': 'VALUE',
+        'value': sentinel_val,
+    })
+    failures.append({
+        'request_put': {
+            'key': sentinel_key,
+            'value': sentinel_val,
+        }
+    })
+
     txn = {
         'compare': compares,
         'failure': failures,