Added Test Definitions for Extension Tests
Added Test Definitions for Extension Tests

1. Os Patching Extension Test
2. VM Diagnostic Extension Test
+ Updated test cycle : EXTENSION
+ Updated single VM sizes for ARM deployment.

v-sirebb/azure-linux-automation,Nidylei/azure-linux-automation,v-sirebb/azure-linux-automation,konkasoftci/azure-linux-automation,FreeBSDonHyper-V/azure-freebsd-automation,hglkrijger/azure-linux-automation,FreeBSDonHyper-V/azure-freebsd-automation,FreeBSDonHyper-V/azure-freebsd-automation,hglkrijger/azure-linux-automation,hglkrijger/azure-linux-automation,iamshital/azure-linux-automation,v-sirebb/azure-linux-automation,konkasoftci/azure-linux-automation,konkasoftci/azure-linux-automation,iamshital/azure-linux-automation,Nidylei/azure-linux-automation,iamshital/azure-linux-automation,Nidylei/azure-linux-automation