Add new object_storage capabilities as advisory

Based on our analysis [1], there were several object_storage tests
available which weren't included in any interop guideline.
This commit adds those tests under a few new capabilities which
are added as advisory for now. They can be moved to required
after one cycle being under advisory. Interop WG will review
these tests for inclusion for the next guideline cycle.

[1] https://etherpad.opendev.org/p/refstack-test-analysis

Change-Id: Ib975b1e116f7ba63ea7a04676a46995a92977adb

guidelines/next.json

@@ -1979,6 +1979,36 @@
        }
       }
       },
+      "objectstore-account-update": {
+      "achievements": [
+       "deployed",
+       "tools",
+       "clients",
+       "future",
+       "complete",
+       "stable",
+       "discover",
+       "doc",
+       "foundation",
+       "atomic",
+       "proximity"
+      ],
+      "admin": false,
+      "description": "",
+      "project": "swift",
+      "required_since": "2021.07",
+      "tests": {
+       "tempest.api.object_storage.test_account_services.AccountTest.test_update_account_metadata_with_create_metadata_key": {
+         "idempotent_id": "id-64fd53f3-adbd-4639-af54-436e4982dbfb"
+       },
+       "tempest.api.object_storage.test_account_services.AccountTest.test_update_account_metadata_with_delete_metadata": {
+         "idempotent_id": "id-9f60348d-c46f-4465-ae06-d51dbd470953"
+       },
+       "tempest.api.object_storage.test_account_services.AccountTest.test_update_account_metadata_with_delete_metadata_key": {
+         "idempotent_id": "id-d4d884d3-4696-4b85-bc98-4f57c4dd2bf1"
+       }
+      }
+      },
       "objectstore-account-list": {
       "achievements": [
        "deployed",