[Placement Group] Add support to associate VM with placement group

[bgriddaluru]

1. Add Placement group field in Spec of AzureStackHCIMachine and AzureStackHCIVirtualMachine CRs
2. (AzureStackHCI) Machine controller will pass down the intent to VirtualMachine via CR and VirtualMachine controller will use the placement group field in VM Spec, if the placement group name is non-empty

Notes: Workflow to Availability Set i.e. placement group lifecycle is managed by cloud-operator.