feat: add exit code in container deletion events

[sambhav-jain-16]

What

Container deletion events now include the container's exit code in the event data.
Fixes: #3722

Why

Users need to understand why containers terminated (success vs error vs signal). Exit codes provide critical debugging information for container lifecycle management and monitoring.

How

• Added GetExitCode() method to ContainerHandler interface
• Added ContainerDeletionEventData struct with ExitCode field to event system
• Modified destroyContainer() to retrieve exit code before calling Stop()
• Implemented for docker, containerd, and podman (uses runtime inspect APIs)
• CRI-O and Raw handlers return errors (not supported by those runtimes)
• Exit code defaults to -1 if unavailable (container still running, retrieval fails, etc.)

Testing

• Unit tests for docker, containerd, and manager
• Integration test validates end-to-end flow

API Example

  {
    "event_type": "containerDeletion",
    "container_name": "/docker/abc123",
    "event_data": {
      "container_deletion": {
        "exit_code": 1
      }
    }
  }

[dims]

@sambhav-jain-16 which container engines did you fully test this on? (containerd only?)

[sambhav-jain-16]

@dims
This is tested on docker and containerd engines and is running already for some time in our setup.

(Not exactly the same code, but we are consuming the current deletion events and then hitting the same docker/containerd APIs to get the exit code)