Add support for model specific job submission scripts

[Schlevidon]

Added support for model specific job submission scripts:

• HQ job submissions now use hq_scripts/job_<model_name>.sh if such a file exists and hq_scripts/job.sh as a default otherwise.
• There is an option to always use the default job script, which is currently only used by the initial HQ job that determines the available models.
  • Therefore, the default hq_scripts/job.sh file is still always required! ⚠️
  • The load balancer will throw an exception if the default hq_script/job.sh file doesn't exist.

Possible issues:

• There is currently no protection against typos in the name of a model specific job submission script. ⚠️
  • Could add console output whenever a fallback to the default job submission script occurs. However, this would clutter the output a lot.
  • Best solution would probably be to add proper logging, but that would be a bigger project (not a priority at the moment).

[linusseelinger]

Looks good to me!
What do you think about the empty string model name point?