Nomad Agent Eligibility for Deployments

[mpass99]

We already have a service that makes the Nomad Agent eligible again after a restart. However, we do not make it ineligible before draining as suggested officially.
This might be obsolete, as our deployments no longer restart all agents together but after each other.

• Check if the agents get ineligible on a restart automatically
• Consider making the Nomad Agents ineligible in Deployments before restarting them.

[MrSerth]

I thought that the Nomad agent is set to ineligible due to the leave_on_interrupt, leave_on_terminate, and drain_on_shutdown settings. However, it might be a good idea to validate that understanding once again.