Export-AzAutomationRunbook : To export an Azure Automation runbook to a Python(.py) file.

### Description of the new feature

Currently Export-AzAutomationRunbook cmd is able to export runbook to a wps_2 script (.ps1 ) file, for wps_2 or wps_2 Workflow runbooks, or to a graphical runbook (.graphrunbook) file, for graphical runbooks.

An update is required to export .py extension files.

We had a scenario to export python runbooks and when we used this command, instead of exporting .py files, .ps1 files were exported.

### Proposed implementation details (optional)

_No response_

Start at the Export-AzAutomationRunbook command and trace how it chooses the output extension for each runbook type. Reproduce the reported case with a Python runbook, then verify that export produces a .py file rather than a .ps1 file and add regression coverage if the command's tests are available.

Written by the indexing model from the issue text.