Standalone Slurm exporter - No Kubernetes needed

[mateusclira-nv]

Summary

Add a minimal, backward-compatible path to run the exporter against a standalone Slurm cluster (slurmrestd with rest_auth/jwt)—no Kubernetes required.

Changes

• New Flags
  • --standalone: skip k8s client/JWT flow.
  • --static-token (optional): alternative to env; CLI still has highest precedence.
• Auth
  • Prefer SLURM_EXPORTER_TOKEN from the environment for REST calls.
  • Do not rely on SLURM_JWT (kept out to avoid collisions with Slurm internals).
• HTTP client
  • Use Header.Set instead of Header.Add for X-SLURM-USER-TOKEN (and Content-Type) to avoid duplicate headers on retries.
• Docs
  • README section describing standalone mode usage, and troubleshooting.

Testing

• Verified with Slurm 24.05.x + slurmrestd v0.0.40.

[Copilot]

Pull Request Overview

This PR adds standalone mode support to the Slurm exporter, allowing it to run without Kubernetes dependencies by using static JWT tokens for authentication with slurmrestd.

• Introduces --standalone and --static-token flags for non-Kubernetes deployments
• Updates HTTP client to use Header.Set instead of Header.Add to prevent duplicate headers on retries
• Adds retry configuration to the default HTTP client for improved reliability

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
cmd/exporter/main.go	Adds standalone mode flags, optional Kubernetes client initialization, and static token issuer
internal/slurmapi/client.go	Improves HTTP client with retry configuration and fixes header handling to prevent duplicates

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[ali-sattari]

Linter is unhappy about go fmt and there is one comment from Copilot that I kept, please address those.