make the script backward compat

packages/extensions/openapi-to-typespec/convert.ps1

@@ -14,10 +14,6 @@ param(
     [string]
     # Specifies the swagger config file, not the swagger json, but the readme config.
     $swaggerConfigFile,
-    [Parameter(Mandatory)]
-    [string]
-    # Specifies the corresponding autorest.md file in azure-sdk-for-net repo used by autorest.csharp codegen.
-    $csharpAutorestFile,
     [string]
     # Specified the output folder, deafult to current folder.
     $outputFolder,
@@ -26,12 +22,18 @@ param(
     $csharpCodegen = "https://aka.ms/azsdk/openapi-to-typespec-csharp",
     [string]
     # Specified the converter codegen, default to https://aka.ms/azsdk/openapi-to-typespec.
-    $converterCodegen = "."
-)
+    $converterCodegen = ".",
+    [string]
+    # Specifies the corresponding autorest.md file in the azure-sdk-for-net repo so that the convert will load it instead of the swagger config file when generating metadata which would include more csharp configurations (i.e. rename rules)
+    $csharpAutorestFile = "")
 
 function GenerateMetadata ()
 {
     Write-Host "##Generating metadata with csharp codegen in $outputFolder with $csharpCodegen"
+    if($csharpAutorestFile -eq "")
+    {
+        $csharpAutorestFile = $swaggerConfigFile
+    }
     $cmd = "autorest --version=3.10.1 --csharp --isAzureSpec --isArm --max-memory-size=8192 --use=`"$csharpCodegen`" --output-folder=$outputFolder --mgmt-debug.only-generate-metadata --azure-arm --skip-csproj $csharpAutorestFile"
     Write-Host "$cmd"
     Invoke-Expression  $cmd