Killed sessions do not get closed

[mehrdad-khojastefar]

Describe the bug
When a boundary session is not gracefully terminated the session remains in the status that it was.

To Reproduce
Steps to reproduce the behavior:

1. Run boundary connect to initialize a session.
2. Run ps aux | grep boundary connect to get the PID of the boundary session related process.
3. Run kill -9 <PID> to kill the process.

Expected behavior
Now since we have not activated any channels for this session the session is stuck in pending state and we should close it manually. If there are any channels active for this session the session remains in the active state.