[DRAFT][WiP][PoC] Operator: IPAM IPAddressClaim & IPAddress request and management

[fgiudici]

This PR introduces an opinionated experimental CAPI IPAM provider resources management in the Elemental Operator:

• the MachineRegistration Spec now has a network field to hold an optional reference to an InClusterIPPool resource (the user should create the InClusterIPPool and reference it in the MachineRegistration)
• on registration, the elemental-operator creates an IPAddressClaim from the InClusterIPPool and references it in the MachineInventory it creates
• the MachineInventory reconcyler references the IPAddress created by the IPAM provider in the new .Status.IPAddressRef as soon as it is available
• the MachineInventory reconcyler returns the IPAddress on MachineInventory deletion by deleting the associated IPAddressClaim

Resource creation/destruction worked in a Rancher test environment with the CAPI IPAM provider installed.

The idea was than to extend the websocket protocol to allow the client to ask the assigned IP address: the elemental-operator server should check the MachineInventory.Status.IPAddressRef and if available get the info from there: this part is completely missing.

[fgiudici]

Superseded by #793 , closing