[GuideLLM Refactor] Reenablement of scenarios and fixes for benchmark package and CLI pathways (#414)

## Summary

Changed the benchmarking entrypoint to take in an Args object which is
now used to load scenarios. It enables a single source of truth in
addition to being able to save the exact configurations in the report
output.

## Details

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## Test Plan

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## Related Issues

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- Resolves #

---

- [ ] "I certify that all code in this PR is my own, except as noted
below."

## Use of AI

- [ ] Includes AI-assisted code completion
- [ ] Includes code generated by an AI application
- [ ] Includes AI-generated tests (NOTE: AI written tests should have a
docstring that includes `## WRITTEN BY AI ##`)

Author: markurtz

pyproject.toml

@@ -9,6 +9,7 @@ include = ["*"]
 
 [tool.setuptools.package-data]
 "guidellm.data" = ["*.gz"]
+"guidellm.benchmark.scenarios" = ["*.json", "**/*.json"]
 
 [tool.pdm]
 distribution = true