GeezerVison

* Fix Get-EnvironmentInformation IsCoreCLR logic
Replace $Runtime = [System.Runtime.InteropServices.RuntimeInformation]  and $OSPlatform = [System.Runtime.InteropServices.OSPlatform]  with ($PSVersionTable.ContainsKey("PSEdition") -and $PSVersionTable.PSEdition -eq "Core").

* Add Response Controller

* [Feature] Replace HttpListener Response tests with WebListener

* Disable Requisiste URLs tests

* Add retry for the URL tests

…ll#5591)

…PowerShell#5586)

- Update contribution guidelines to make updating the changelog required
- add a checklist to PR template

Comment by @SteveL-MSFT :
> Everyone should understand that we are always open to feedback and nothing is set in stone. Based on a team discussion, one of the biggest costs for a release is creating the ChangeLog hence updating this document to push it to the contributor most aware of why the changes are being made and ideally how it's useful to end users.