$TriggerMetadata.sys is not populated anymore

### Problem

According to the [documentation](https://docs.microsoft.com/en-us/azure/azure-functions/functions-reference-powershell?tabs=portal#triggermetadata-parameter), `$TriggerMetadata` is supposed to be populated as follows:

Property | Description | Type
-- | -- | --
UtcNow | When, in UTC, the function was triggered | DateTime
MethodName | The name of the Function that was triggered | string
RandGuid | a unique guid to this execution of the function | string

In the latest Functions runtime version, the `sys` member is absent.

### Temporary Workaround

Pin your Functions runtime to the previous version. In order to do that, please set the `FUNCTIONS_EXTENSION_VERSION` app setting to `3.0.14413`.

### Fix

This is a recent regression caused by some Host/Worker traffic optimizations. In order to adapt to these changes, the PowerShell worker is supposed to populate `sys`, similarly to how the Node.js worker does it: https://github.com/Azure/azure-functions-nodejs-worker/commit/695a274f392af49eab75780abfbba1ea3b445814

Consider adding an automated integrations test for the Host.