HelmInstaller: pick latest stable Helm by excluding prerelease/drafts#491

mot256 wants to merge 2 commits intomicrosoft:mainmicrosoft/azure-pipelines-tasks-common-packages:mainfrom

mot256:fix/helminstaller-prerelease-filtermot256/azure-pipelines-tasks-common-packages:fix/helminstaller-prerelease-filterCopy head branch name to clipboard