Bring all of our powershell scripts into compliance with our best practices

Not all of our scripts follow the best practices outlined [here](https://github.com/dotnet/arcade/blob/master/Documentation/Policy/PowershellBestPractices.md).

We should do the work to bring them into compliance. This could possibly include some breaking changes, so whoever takes this should do some investigation to see if any changes implemented break things for other repos.