[ASP-4238] Add on-site submission support

[fschuch]

What

• Add support for on-site submissions:
  • SBATCH_PATH is set on the CLI, so it is expected to download job-script files, submit them to slurm using sbatch, and include slurm_job_id on the payload to create a new submission.
  • The API processes the creation giving it the status SUBMITTED and adding the new entry on the database. No need to parse any job-property, since all #SBATCH directives were processed at submission time by sbatch.
  • These jobs won't be processed as pending by the agent since their status is not CREATED, remember it was already submitted.
  • Like on remote submissions, the agent will keep track of active jobs (STATUS=SUBMITTED) and update them as needed.

Why

As a Jobbergate maintainer, I want to add support for on-site submissions to the next-gen Jobbergate, so that it can operate with feature parity compared to the legacy system, thereby facilitating user-base migration. Meanwhile, current support for remote submissions will remain undisturbed.

Task: https://jira.scania.com/browse/ASP-4238

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[dusktreader]

One minor comment for you. Nice work!