test(ui): update sign-up tests to use E2E_NEW_PASSWORD environment variable

- Modified the sign-up test to retrieve the password from the E2E_NEW_PASSWORD environment variable.
- Updated documentation to specify the requirement for the E2E_NEW_PASSWORD variable before running tests.

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

@@ -18,6 +18,7 @@ jobs:
       AUTH_TRUST_HOST: true
       NEXTAUTH_URL: 'http://localhost:3000'
       NEXT_PUBLIC_API_BASE_URL: 'http://localhost:8080/api/v1'
+      E2E_NEW_PASSWORD: ${{ secrets.E2E_NEW_PASSWORD }}
     steps:
       - name: Checkout repository
         uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0