Add task `Package_External_Help_Documentation`

[johlju]

There might be use cases for a task Package_External_Help_Documentation that packages the help documentation in a .cab file according to this: https://learn.microsoft.com/en-us/powershell/utility-modules/platyps/create-help-using-platyps?view=ps-modules#creating-an-updateable-help-package

Suggest trying to use a release asset for this GithubConfig in build.yaml:

https://github.com/gaelcolas/Sampler.GitHubTasks/blob/1f288c3bc35ab124ff9f8a8f405111c10761744e/.build/tasks/New-Release.GitHub.build.ps1#L147-L164