IaaS: add security group to server not supported #1216

Problem description

It's currently not possible to add a security group to a server.

One must either do stackit curl or use stackit network-interface update --security-groups (but that must get passed all desired sec groups)

Proposed solution

Implement a stackit server security-group attach (and also detach) command.

This is already possible via the IaaS API: https://docs.api.eu01.stackit.cloud/documentation/iaas/version/v2#tag/Servers/operation/v2AddServerSecurityGroup

Is there already a general plan on how the IaaS API should be integrated into the STACKIT CLI? Currently only half of the endpoints are directly available in the CLI. Sadly most of these endpoints are preventing me from fully moving over from the openstack CLI.