SQL IaaS Powershell cmdlets

SQL IaaS Powershell cmdlets
 Scenarios:
 1) Gets current SQL IaaS’s guest agent extensions configuration 
 2) Sets SQL IaaS’s guest agent extensions configuration 
 - Enable/ Disable / Configure Auto-patching settings
 - Enable/ Disable / Configure Auto-backup settings
 3) Removes SQL IaaS’s guest agent extension. 

Test cases:
•Added functional tests for SqlIaaSAgent extension

[nitpick] I think you don't have to define this function here, and you can just move the codes to ```ProcessRecord()```. There are some legacy debt about this.