Implemented JavaScript example for configuring Gemini model parameters

[cestercian]

This PR adds a new JavaScript example demonstrating how to configure model parameters for the Gemini API.

Features

• Adds configure_model_parameters.js showing how to:

  • Set candidate count
  • Configure stop sequences
  • Limit output tokens
  • Adjust temperature for generation

• Includes:

  • Main example file with proper region tags and documentation
  • Test file with basic validation
  • Updated package.json with new run script
  • Updated README.md with example documentation

The implementation follows the repository's style guide with proper region tags, copyright headers, and matches the functionality of the Python equivalent.

This example helps developers understand how to fine-tune Gemini model outputs by configuring various generation parameters.