BZ#2192851 [RFE] Make use of OVN Load Balancer Groups

OVN supports a new table "Load_Balancer_Group" that allows to group load balancers to enable CMS to group them and simplify its management. This has been used for scaling purposes on ovn-kubernetes.

OVN-Octavia provider could take advantage of this so that new loadbalancers do not need to be associated to the LR and all its associated LSs, but to only add them to the relevant group (e.g., one group per LR)