Dynamically supervise a GRPC connection and keep it alive for a while,
using a timeout to kill the process on inactivity.
The Connection GenServer keeps the connection alive, while listening to
a health stream from the GRPC endpoint, notifying any subscribed
listeners about changes to health.
This health is then propagated to the main servers page.
Also create a looping get_sys_info which retrieves some basic system
information.
`Prymn.Agent.Connection` GenServer uses healthchecking with the new
streaming RPC, retrieving asynchronously the health status of the agent.
The Connection will also shut itself down when there's no usage (when
the keepalive function is not called frequently)
