List all the App Service Slots for a given App Service Plan

**Related command**

`az webapp list --query "[?appServicePlanId=='$appServicePlanID']"`

**Is your feature request related to a problem? Please describe.**

I do have a requirement to change the vnet integration for all my applications to move to a new subnet. And, I was hoping to list all the web apps (app services) and corresponding slots in an app service plan - run through the list iteratively to remove the vnet integration and then associate it back.

**Describe the solution you'd like**

Similar to the command posted above, where I can list all the app services in a given plan - would like to have the same feature for `az webapp deployment slot`

**Describe alternatives you've considered**

I was trying my luck with `az resource list`, while I can list my app service and their corresponding slots with this command I cannot restrict it to a specific app service plan.

`az resource list --resource-group $resourceGroupName --query "[?kind=='app,linux' && (type=='Microsoft.Web/sites' || type=='Microsoft.Web/sites/slots')]"`

**Additional context**