Added Custom Header Test in Cypress

[belaletech]

Summary

• Added a new test to validate custom headers in Cypress.
• The test sends a GET request to https://httpbin.org/headers with a custom header (x-custom-header).
• Validates that the response contains the expected custom header.

Changes

• Added custom-header.spec.js under cypress/integration/examples/.
• Updated the README.md to include the new test in the documentation.

Testing

• Successfully executed the test locally using Cypress.
• Verified that the response contains the correct custom header.

Please review and let me know if any changes are needed. 🚀