Slurm client version compatibility in the sidecar image

[matbun]

The interlink-sidecar-slurm image ships Slurm client tools (sbatch, squeue, scancel, sinfo)
from AlmaLinux 9 default packages (currently Slurm 22.05). This version is incompatible with
newer Slurm clusters due to wire protocol changes between major versions.

For example, when the sidecar (22.05) connects to a Slurm 25.11 cluster (e.g. deployed via the
Slinky slurm-operator), sbatch fails with:

sbatch: error: Batch job submission failed: Insane message length

Additionally, the auth/slurm plugin (introduced in Slurm 23.11) and the JSON serializer
(serializer_json.so) are not built by default because the RPM spec requires --with jwt
and --with slurmrestd flags along with libjwt-devel and json-c-devel build dependencies.

Problem

• The sidecar image is tightly coupled to a specific Slurm version but does not document or
  test which cluster versions it supports.
• Users targeting newer Slurm clusters (23.11+, 24.x, 25.x) must build custom images, which
  is not straightforward (requires source builds with specific flags).
• There is no CI to verify compatibility across Slurm versions.

Proposal

• Publish sidecar images for multiple Slurm versions (e.g. interlink-sidecar-slurm:slurm-24.05,
  interlink-sidecar-slurm:slurm-25.11) or parametrize the Dockerfile with an ARG SLURM_VERSION.
• Build Slurm from source with --with jwt --with slurmrestd to include auth_slurm.so,
  auth_jwt.so, and serializer_json.so.
• Add integration tests that verify sbatch, sinfo, and job submission against different
  Slurm cluster versions.
• Document supported Slurm versions in the README.

I can help with this, if needed. Let's just agree on a plan.
Some templating for flexible SLURM version already introduced here: matbun@e04d9d3