[windows] Change packer templates from json to hcl (#8999)

images.CI/linux-and-win/azure-pipelines/windows2019.yml

@@ -18,4 +18,4 @@ jobs:
   parameters:
     image_type: windows2019
     image_readme_name: Windows2019-Readme.md
-    image_template_name: windows-2019.json
+    image_template_name: windows-2019.pkr.hcl

images.CI/linux-and-win/azure-pipelines/windows2022.yml

@@ -18,4 +18,4 @@ jobs:
   parameters:
     image_type: windows2022
     image_readme_name: Windows2022-Readme.md
-    image_template_name: windows-2022.json
+    image_template_name: windows-2022.pkr.hcl

images.CI/linux-and-win/build-image.ps1

@@ -22,8 +22,6 @@ if (-not (Test-Path $TemplatePath))
 $ImageTemplateName = [io.path]::GetFileName($TemplatePath).Split(".")[0]
 $InstallPassword = [System.GUID]::NewGuid().ToString().ToUpper()
 
-packer validate -syntax-only $TemplatePath
-
 $SensitiveData = @(
     'OSType',
     'StorageAccountLocation',
@@ -37,6 +35,12 @@ $SensitiveData = @(
 Write-Host "Show Packer Version"
 packer --version
 
+Write-Host "Download packer plugins"
+packer init $TemplatePath
+
+Write-Host "Validate packer template"
+packer validate -syntax-only $TemplatePath
+
 Write-Host "Build $ImageTemplateName VM"
 packer build    -var "client_id=$ClientId" `
                 -var "client_secret=$ClientSecret" `