Support PVE 8's updated Memory typing

[gecgooden]

It looks like PVE 8 now returns a string for the memory property, as opposed to an int from previous versions.
This change makes it so that the unmarshalling will convert from a string to an int automatically so this should work for current and older versions

[bcm820]

@sp-yduck Can this PR be prioritized? I'm encountering the same issue with PVE 8 and am unable to provision any more VMs until this is patched:

E0621 03:04:19.875458       1 controller.go:324] "Reconciler error" err="json: cannot unmarshal string into Go struct field VirtualMachineConfig.memory of type int" controller="proxmoxmachine" controllerGroup="infrastructure.cluster.x-k8s.io" controllerKind="ProxmoxMachine" ProxmoxMachine="default/kubenet-md-0-pp5vl-7mqwk" namespace="default" name="kubenet-md-0-pp5vl-7mqwk" reconcileID=7845a60f-a1fa-4eb1-82c4-60103e4938c9
E0621 03:04:25.873166       1 reconcile.go:126] "failed to get vm config" err="json: cannot unmarshal string into Go struct field VirtualMachineConfig.memory of type int" controller="proxmoxmachine" controllerGroup="infrastructure.cluster.x-k8s.io" controllerKind="ProxmoxMachine" ProxmoxMachine="default/kubenet-md-0-pp5vl-hzzcc" namespace="default" name="kubenet-md-0-pp5vl-hzzcc" reconcileID=87988968-e116-4901-9557-e472d8c5a0ab
E0621 03:04:25.873239       1 proxmoxmachine_controller.go:160] "Reconcile error" err="json: cannot unmarshal string into Go struct field VirtualMachineConfig.memory of type int" controller="proxmoxmachine" controllerGroup="infrastructure.cluster.x-k8s.io" controllerKind="ProxmoxMachine" ProxmoxMachine="default/kubenet-md-0-pp5vl-hzzcc" namespace="default" name="kubenet-md-0-pp5vl-hzzcc" reconcileID=87988968-e116-4901-9557-e472d8c5a0ab

[sp-yduck]

@gecgooden @bcm820
sorry I had missed this PR. thank you for making this. I have made a release for this change v0.0.0-alpha28
could you also open a PR for cluster api side ? then I will merge and publish a new release.