Add nightly benchmarking documentation

[kaushikmitr]

This pull request updates the regression testing documentation to enhance clarity, improve formatting, and introduce a new section on nightly benchmarking. The most important changes include reformatting test case descriptions, adding details about traffic distribution and metrics expectations, and documenting the nightly benchmarking process.

Documentation Improvements:

• Reformatted Test Case Details: Improved readability for test cases by using clearer formatting, such as bullet points and percentages for traffic distribution in the multi-LoRA test case. Updated terminology for request rates (QPS) and added clarity to dataset descriptions.
• Enhanced Metrics Expectations: Clarified expectations for regression analysis metrics, including R² values for prompts and latency, with minor variance allowances.

New Nightly Benchmarking Section:

• Nightly Benchmarking Pipeline: Added a detailed description of the automated nightly benchmarking process, including datasets used, benchmarking steps, and alerting mechanisms for regression detection.

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[k8s-ci-robot]

Hi @kaushikmitr. Thanks for your PR.

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[ahg-g]

/ok-to-test

[kfswain]

Looks great! Thanks for all the work here, this is hugely beneficial.

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kaushikmitr, kfswain

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[kaushikmitr]

/retest