Add utilitiy integration test to clean up test users in account (#3665)

## Changes
Add utility integration test to clean up test users in account. The test
users in the account are not deleted by our clean up system. If there
are many users, the API becomes slower, increasing the likelihood of
timeouts for our integration tests. This utility test cleans up the test
users. Given that it might interfere with other tests and its nature to
delete account resource, it is disabled from running by default.

### Linked issues

Resolves #3497
Resolves #3547

### Tests

- [x] added utility integration tests

tests/integration/account/test_account.py

@@ -9,6 +9,21 @@
 from databricks.labs.ucx.account.workspaces import AccountWorkspaces
 
 
+@pytest.mark.skip(reason="Test tests interferes with other tests")
+def test_clean_test_users_in_account(acc: AccountClient) -> None:
+    """Run this test to clean up the account from test users.
+
+    Watchdog does not clean up the account from test users as it only looks
+    at the workspace level. This test is not really a test, but a test
+    utility to clean up the account from test users.
+    """
+    for user in acc.users.list(attributes="id", filter='displayName sw "dummy-"'):  # "sw" is short for "starts with"
+        if user.id:
+            acc.users.delete(user.id)
+    # No assert as the API is eventually consistent and this test is skipped
+    # Verify manually instead
+
+
 @pytest.fixture
 def clean_account_level_groups(acc: AccountClient):
     """Clean test generated account level groups."""