Add arcade infrastructure

eng/common/darc-init.ps1

@@ -0,0 +1,21 @@
+$verbosity = "m"
+. $PSScriptRoot\tools.ps1
+
+function InstallDarcCli {
+  $darcCliPackageName = "microsoft.dotnet.darc"
+  $dotnet = "$env:DOTNET_INSTALL_DIR\dotnet.exe"
+  $toolList = Invoke-Expression "$dotnet tool list -g"
+
+  if ($toolList -like "*$darcCliPackageName*") {
+    Invoke-Expression "$dotnet tool uninstall $darcCliPackageName -g"
+  }
+
+  $toolsetVersion = $GlobalJson.'msbuild-sdks'.'Microsoft.DotNet.Arcade.Sdk'
+
+  Write-Host "Installing Darc CLI version $toolsetVersion..."
+  Write-Host "You may need to restart your command window if this is the first dotnet tool you have installed."
+  Invoke-Expression "$dotnet tool install $darcCliPackageName --version $toolsetVersion -v $verbosity -g"
+}
+
+InitializeTools
+InstallDarcCli