Azure powershell cmdlets for SQLVM extension

Powershell cmdlets for SQL-IaaS VM to configure management features in SQL VM deployment. 

The scope of SQL IaaS Powershell Cmdlet covers the following:
•	Gets current SQL IaaS’s guest agent extensions configuration 
•	Sets SQL IaaS’s guest agent extensions configuration 
o	      Enable/ Disable / Configure Auto-patching settings
o	      Enable/ Disable / Configure Auto-backup settings
•	Removes SQL IaaS’s guest agent extension configuration

Please check with @guangyang whether SecureString is needed here.