Add validation section for TensorRT models

[sreelekha-ira]

Added a section on validating TensorRT models before deployment, including an example command.

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[sreelekha-ira]

Summary

Adds a documentation section describing how to validate a TensorRT .plan model
using Model Navigator before deployment with Triton Inference Server.

This improves onboarding for new users and provides a minimal example for
verifying TensorRT plans with expected input shapes.

What this PR does

• Adds a new subsection titled "Validating a TensorRT Model Before Deployment"
  under the relevant documentation page.
• Provides a practical model-navigator validate command example.
• Lists the key parts of the validation output to help users understand results.
• Improves discoverability of TensorRT model validation workflows.

Motivation

Many Triton users ask how to verify their TensorRT models before packaging them
into a Triton model repository. This PR gives them a simple, copy-and-paste
example using Model Navigator.

Testing

• Verified that the new Markdown section renders correctly using GitHub's preview.
• Confirmed that the example command matches the current Model Navigator CLI.
• Reviewed for formatting consistency with existing documentation.

Additional Notes

This is a pure documentation update. No code changes or functional updates are made.