[release/v13] Support Openstack Server Groups to ensure affinity when deploying Rancher nodes

[github-actions]

Backport #1981 to release/v13 for #1982

Copied from PR:

Addresses #1701

release/v13

Description

Adding support to the Openstack Cloud Provider used within the rancher2_machine_config_v2 resource

Testing

I have forked this and created a provider under https://search.opentofu.org/provider/geoffr/rancher2/latest and tested both the id and names for the server group successfully on a deployed Rancher RKE2 cluster.

As these are optional fields this is not a breaking change.