[ubuntu] Change packer templates from json to hcl (#8991)

* [ubuntu] Change packer tempaltes from json to hcl

* Add packer init

* Fix variable types for Ubuntu20 template

Author: shamil-mubarakshin

helpers/GenerateResourcesAndImage.ps1

@@ -25,7 +25,7 @@ Function Get-PackerTemplatePath {
             $relativeTemplatePath = Join-Path (Join-Path "windows" "templates") "windows-2022.pkr.hcl"
         }
         ([ImageType]::Ubuntu2004) {
-            $relativeTemplatePath = Join-Path (Join-Path "ubuntu" "templates") "ubuntu-20.04.json"
+            $relativeTemplatePath = Join-Path (Join-Path "ubuntu" "templates") "ubuntu-20.04.pkr.hcl"
         }
         ([ImageType]::Ubuntu2204) {
             $relativeTemplatePath = Join-Path (Join-Path "ubuntu" "templates") "ubuntu-22.04.pkr.hcl"

images.CI/linux-and-win/azure-pipelines/ubuntu2004.yml

@@ -18,4 +18,4 @@ jobs:
   parameters:
     image_type: ubuntu2004
     image_readme_name: Ubuntu2004-Readme.md
-    image_template_name: ubuntu-20.04.json
+    image_template_name: ubuntu-20.04.pkr.hcl