Add Placement Group Server Action

[CubitsDev]

Affects:

Server Actions

Need for this:

Links the placement group server action API

Hetzner API documentation

https://docs.hetzner.cloud/#server-actions-add-a-server-to-a-placement-group

Tasks

• Implement method on Server class
• Add new Action enum
• Implement change in ServerChangeListener
• Implement change in ServerService
• Add testing