Implement mechanism to ensure all agents are properly registered at the start of Vulnerability Detection tests

[Rebits]

Description

Vulnerability Detection E2E tests are currently impacted by a known issue, causing intermittent connection failures for certain agents. For more details, please refer to this issue

To mitigate potential false positives, I recommend creating a fixture that ensures all agents are properly connected and registered before proceeding with the tests. If any agents fail to connect, the tests should be aborted.

Tasks

• Create a fixture to ensure all agents are registered before Vulnerability Tests start

[Rebits]

Planned to be fixed in #5698