[Bug]: Warnings when terminating Verda instances while provisioning

[r4victor]

Steps to reproduce

1. Create a fleet with Verda instances.
2. Terminate fleet while instances are in provisioning state in Verda console.
3. See dstack Warnings as Verda backend does not handle the exception:

           WARNING  dstack._internal.server.background.pipeline_tasks.instances.terminatio
                    n:64 Failed to terminate instance cloud-fleet-2-5. Will retry. Error:
                    APIException('forbidden_action', "Can't discontinue a provisioning
                    instance")

Actual behaviour

No response

Expected behaviour

Handle the exception and propagate an expected error to the instance pipeline so that deletion attempts are retried without warnings.

dstack version

master

Server logs

Additional information

No response