[Feature request]: Create a cmdlet Get-AzApiManagementProductByGroup

I noticed that we have [Add-AzApiManagementProductToGroup](https://docs.microsoft.com/en-us/powershell/module/az.apimanagement/add-azapimanagementproducttogroup?view=azps-2.5.0) and [Remove-AzApiManagementProductToGroup](https://docs.microsoft.com/en-us/powershell/module/az.apimanagement/remove-azapimanagementproductfromgroup?view=azps-2.5.0), but if it's possible to create a cmdlet like `Get-AzApiManagementProductByGroup` to query the products by group Id/Name? for example I want to list all the products in "Developers" group, it's impossible at present.

Besides, I found the Access Control information isn't included in [Get-AzApiManagementProduct](https://docs.microsoft.com/en-us/powershell/module/az.apimanagement/Get-AzApiManagementProduct?view=azps-2.5.0)--> [PsApiManagementProduct Class](https://docs.microsoft.com/en-us/dotnet/api/microsoft.azure.commands.apimanagement.servicemanagement.models.psapimanagementproduct?view=azurerm-ps), it's inconvenient. If Access Control information is included, it's possible to filter with pipe like below, in this situation, it's unnecessary to create a new cmdlet like `Get-AzApiManagementProductByGroup`
```powershell
Get-AzApiManagementProduct -Context $ApimContext | Where-Object GroupName -EQ "Developers"
```