In qemu the 'volume' key maps to 'file', both can be used,
so to support this case in the comma-separated property
list parser we need a way to alias keys to one another.
This allows declaring a key like:
volume => {
alias => 'file'
}
file => {
type => 'string',
format => 'pve-volume-id',
default_key => 1,
format_description => 'volume'
}
With this the following property strings are equivalent and
result in the same datastructure being returned from
parse_property_string: