Fetch and set defaults for plugins

[hbagdi]

Currently, default values for plugins need to be hard-coded into the YAML file.
It would be nice if users can set only the values they need in the file and then the rest of the defaults is something deck figures out on it's own.

Kong Ingress Controller already does something similar to this.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.