test(ui): implement GitHub OAuth flow for social sign-up

- Added support for GitHub social login in the sign-up process.
- Updated the sign-up page to include a GitHub login button and related methods.
- Enhanced E2E tests to validate the complete GitHub OAuth flow, ensuring users can authenticate and return to the application successfully.
- Updated documentation to reflect the new test case for GitHub social sign-up.

.github/workflows/ui-e2e-tests.yml

@@ -18,6 +18,8 @@ jobs:
       AUTH_TRUST_HOST: true
       NEXTAUTH_URL: 'http://localhost:3000'
       NEXT_PUBLIC_API_BASE_URL: 'http://localhost:8080/api/v1'
+      E2E_GITHUB_USER: ${{ secrets.E2E_GITHUB_USER }}
+      E2E_GITHUB_PASSWORD: ${{ secrets.E2E_GITHUB_PASSWORD }}
     steps:
       - name: Checkout repository
         uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0