Automation should exist to pull in latest builds of PowerShell into nightly branch

The value in providing this automation is to get the latest PS running with the latest .NET as soon as possible to catch and flush out any issues early giving us more confidence in releases.

The [update-dependencies tool](https://github.com/dotnet/dotnet-docker/tree/master/eng/update-dependencies) can be utilized to update the dockerfiles and create a PR.

`dotnet run --project .\eng\update-dependencies\ -- 5.0 --product-version powershell=7.1.0-preivew.6`

The [update-dependencies pipeline](https://github.com/dotnet/dotnet-docker/blob/master/eng/pipelines/update-dependencies.yml) can be updated to automatically run the tool on a schedule.

In order to complete this work the following needs to be in place for the PS _daily_ builds:

1. Binaries need to be published to a public location
1. Binaries need to be signed
1. Checksums need to be published to a public location