[BUG] Fix ApplicationGatewayKeyVaultSecretException from Istio Gateway Deployment

In Greenfield Azure OSDU deployment, the ApplicationGatewayKeyVaultSecretException was observed during "Service Resource" deployment step resulting to Istio gateway resource created in a failed state. Detail error message:

Error: waiting for create/update of Application Gateway: (Name "xxxx-gw" / Resource Group "xxxx-rg"): Code="ApplicationGatewayKeyVaultSecretException" Message="Problem occured while accessing and validating KeyVault Secrets associated with Application Gateway '/subscriptions/xxxx/resourceGroups/xxxx-rg/providers/Microsoft.Network/applicationGateways/xxxx-gw'. See details below:" Details=[{"code":"0","message":"Operation returned an invalid status code 'Forbidden'"}]