fix(deduplication): A4x-max (slurm) bare metal prolog/epilog scripts

[Neelabh94]

This PR removes the duplicated embedding of the prolog/epilog script in the SLURM A4X BareMetal blueprint and standardizes the process by utilizing the external prolog/epilog scripts, which were being already fetched from slurm-gcp using curl.

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[gemini-code-assist]

Code Review

This pull request refactors the a4xmax-bm-slurm-blueprint.yaml by replacing inline IMEX prolog and epilog scripts with a reference to a controller_startup_script and enabling external prolog/epilog functionality. Feedback indicates a critical issue with a duplicated controller_startup_script key in the YAML, which needs to be resolved to prevent unexpected behavior. Additionally, the slurm_controller module's use block requires an update to include controller_startup to comply with the repository's style guide regarding explicit module dependencies.