Move queue global variables out of job_queue module

[xjules]

In scheduler we still rely on some job_queue globals:

from ert.job_queue.queue import (
    CLOSE_PUBLISHER_SENTINEL,
    EVTYPE_ENSEMBLE_CANCELLED,
    EVTYPE_ENSEMBLE_STOPPED,
)

those should be moved to a either standalone file within the scheduler module and directly into scheduler.py

[xjules]

Relates to #8246