Add a Makefile template to make it easier to run common plugin commands

[daviddavis]

Migrated from https://pulp.plan.io/issues/5107

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Inspired by pulp-smash's Makefile:

https://github.com/pulp/pulp-smash/blob/master/Makefile

It would be nice to have something similar for plugins to provide an easy and standardized way to create commands.

[daviddavis]

Old PR: #278

[stale]

This issue has been marked 'stale' due to lack of recent activity. If there is no further activity, the issue will be closed in another 30 days. Thank you for your contribution!