Update Samples Documentation to use PowerShell

**Problem**
Some of the documented samples have adopted `PowerShell` (see PR: https://github.com/dotnet/dotnet-docker/pull/1584), while others are using `cmd`. This is an inconsistent experience for developers.

**Example**
For instance, the [documentation for the aspnetapp sample](https://github.com/dotnet/dotnet-docker/blob/master/samples/host-aspnetcore-https.md#windows-using-linux-containers) renders the shell examples as `console` but uses `cmd`.

```console
dotnet dev-certs https -ep %USERPROFILE%\.aspnet\https\aspnetapp.pfx -p crypticpassword
```

It would be helpful if there's a `PowerShell` version where applicable (e.g. for Windows).

```powershell
dotnet dev-certs https -ep $env:USERPROFILE\.aspnet\https\aspnetapp.pfx -p crypticpassword
```

**Customer Impact**
Developer friction, especially for those who are 'getting started'.

**Business Value**
Reduce developer friction. Adding clarity to documentation aids adoption.

**Desired Solution**
Consistent documentation across the samples. There could be a `PowerShell` version and a `cmd` version, but overall it would be helpful to adopt a `PowerShell` version of the samples documentation.