CG-12227: Enable deployment of codegen PRs to Vercel

[codegen-sh]

Description

This PR adds the necessary configuration to enable automatic deployment of PRs to Vercel, specifically for the Mintlify documentation site in the docs/ directory.

Changes

• Added vercel.json configuration file for Mintlify docs deployment
• Created GitHub workflow .github/workflows/vercel-pr-deployment.yml to handle PR deployments
• Added documentation in docs/VERCEL_DEPLOYMENT.md with setup instructions

Setup Required

After merging this PR, the following setup is required:

1. Create a Vercel project for the repository
2. Add the required secrets to GitHub:
   • VERCEL_TOKEN
   • VERCEL_ORG_ID
   • VERCEL_PROJECT_ID
3. Ensure Mintlify integration is properly configured

Resolves CG-12227

[CLAassistant]

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