Opt out of the Azure PowerShell in-tool notification for version upgrade feature

[AnatoliB]

In the Azure Functions context, the Azure PowerShell in-tool notification for version upgrade feature is less valuable and potentially dangerous, as it may negatively impact apps performance and reliability. In order to avoid that, the PS Worker should opt out of this feature by setting $env:AZUREPS_CHECK_FOR_UPGRADE to $false automatically, before giving control to customer code or loading any Az PS modules.