[Bug]: Background tasks SELECT all run's job submissions

[r4victor]

Steps to reproduce

1. Create a run with many job submissions (e.g. a retry run that fails to provision due to no offers, may require adjusting _PENDING_RETRY_DELAYS to generate job submissions quickly).
2. It's suspected this can lead to high memory usage but I'm yet to reproduce it locally.

Actual behaviour

These SELECTs may fetch too many rows:

• dstack/src/dstack/_internal/server/background/tasks/process_running_jobs.py

  Line 158 in fae73ce

  .options(joinedload(RunModel.jobs))

• dstack/src/dstack/_internal/server/background/tasks/process_runs.py

  Lines 156 to 157 in fae73ce

  	selectinload(RunModel.jobs)
  	.joinedload(JobModel.instance)

Expected behaviour

Select only the necessary (latest) submissions for every job.

dstack version

master

Server logs

Additional information

No response