Refactor Azure CLI login step to use a single creds JSON string for authentication

Author: Harsh-Microsoft

.github/workflows/gp-test-automation.yml

@@ -36,10 +36,7 @@ jobs:
       - name: Azure CLI Login
         uses: azure/login@v2
         with:
-          client-id: ${{ secrets.AZURE_CLIENT_ID }}
-          client-secret: ${{ secrets.AZURE_CLIENT_SECRET }}
-          subscription-id: ${{ secrets.AZURE_SUBSCRIPTION_ID }}
-          tenant-id: ${{ secrets.AZURE_TENANT_ID }}
+          creds: '{"clientId":"${{ secrets.AZURE_CLIENT_ID }}","clientSecret":"${{ secrets.AZURE_CLIENT_SECRET }}","subscriptionId":"${{ secrets.AZURE_SUBSCRIPTION_ID }}","tenantId":"${{ secrets.AZURE_TENANT_ID }}"}'
 
       - name: Start AKS
         id: start-aks