test(ui): update environment variable name for user password in sign-up tests

- Changed the environment variable name from 'E2E_NEW_PASSWORD' to 'E2E_NEW_USER_PASSWORD' in the UI E2E tests workflow and related documentation.
- This update ensures consistency across the test setup and improves clarity in the sign-up flow tests.

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

@@ -36,7 +36,7 @@ jobs:
       E2E_M365_CERTIFICATE_CONTENT: ${{ secrets.E2E_M365_CERTIFICATE_CONTENT }}
       E2E_KUBERNETES_CONTEXT: 'kind-kind'
       E2E_KUBERNETES_KUBECONFIG_PATH: /home/runner/.kube/config
-      E2E_NEW_PASSWORD: ${{ secrets.E2E_NEW_PASSWORD }}
+      E2E_NEW_USER_PASSWORD: ${{ secrets.E2E_NEW_USER_PASSWORD }}
       
     steps:
       - name: Checkout repository