docs: add GCP Deployment guide in documentation

[ghanshyam2005singh]

📌 Fixes

Closes #496

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📝 Summary of Changes

This pull request adds a new installation guide for deploying KubeStellar on GCP to the documentation landing page. The update ensures users can easily find instructions for setting up KubeStellar in a production environment using GCP.

Documentation improvements:

• Added the documentation of Kubestellar GCP Deployment Guide in src/app/docs/getting-started/gcp-deployment/page.mdx
• Added a link to GCP Deployment Guide in "Install & Configure" section of src/app/docs/page.mdx

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Checklist

Please ensure the following before submitting your PR:

• I have reviewed the project's contribution guidelines.
• I have written unit tests for the changes (if applicable).
• I have updated the documentation (if applicable).
• I have tested the changes locally and ensured they work as expected.
• My code follows the project's coding standards.

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[github-actions]

👋 Hello! @ghanshyam2005singh Welcome to the Kubestellar.

Thank you for submitting your first Pull Request to KubeStellar. We are delighted to have you in our Universe!
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[MAVRICK-1]

looks good !