Use hostname as the default Kubernetes pod name

[estolfo]

Use the hostname as the Kubernetes pod name in the Container Info metadata if the pod id is parsed from /proc/self/cgroup.
This will help solve part of #1292, which is partly due to a server issue and partly due to this missing usage of the hostname as the default pod name in the Ruby agent.

[ghost]

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• Start Time: 2022-10-14T13:42:54.363+0000

• Duration: 29 min 46 sec

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[miltonhultgren]

Thanks for fixing this! I'm not sure if my review means anything here since I don't really understand the details of Ruby or APM Agents.

[trentm]

LGTM (with the caveat that my Ruby is ... poor :)