Armadactl get exectuor/delete executor commands

[robertdavidsmith]

In armadactl, currently you can only cordon and uncordon executors

Ideally there would also be

• An armadactl delete executor command. This would be useful when an executor is retired. Currently, if an executor is retired it stays in the metrics forever unless you manually delete it from the db via sql.
• For completeness, an armadactl get executor command, that returns basic info, would also be useful.

Thanks,

Rob