Update Windows servercore to newer version

Windows Dockerfile:

FROM mcr.microsoft.com/windows/servercore:1809
LABEL Description="Windows Server Core development environment for Wireshark"

Available images on dockerhub.

Windows Server support dates:

RELEASES
Version		Start Date	End Date
Version 20H2	10/20/2020	05/10/2022
Version 2004	05/27/2020	12/14/2021
Version 1909	11/12/2019	05/11/2021
Version 1903	05/21/2019	12/08/2020
Version 1809	10/02/2018	11/10/2020
Version 1803	04/30/2018	11/12/2019
Version 1709	10/17/2017	04/09/2019

There was an issue with debugging Wireshark in vscode on 1809:
Windows 10: Invalid parameter passed to C runtime function. #402

Testing on 20H2 resolved that issue.

Windows Server, version 1909 end of servicing
Should the Dockerfile load 2004 or 20H2?

(Windows 2000 was a great release but would like to have words with Microsoft every time I see Windows 2004 as current version)