Launching parallel tasks

[marksibrahim]

• creates new config_parallel_tasks mirroring config but with additional fields for defining parallel task and app variation combinations
• create a new slurm_cluster mode for launching on slurm
• to ensure launcher works on SLURM updated the executable for the subprocess to use executable='/bin/bash' (thank you AI).

Tested with

1. Check new logic works on SLURM via:

uv run launch_parallel_agents.py mode=slurm_cluster use_wandb=True agent=dummy

2. Check existing launcher works as expected

uv run launch_agent.py mode=local use_wandb=True agent=dummy

[KarenUllrich]

PR is functional for me.
I would probably call them sweeps instead of paralel. WDYT?