I'm not quite sure what do you mean by "generic execution plugin". There is no such functionality in Dynatrace (maybe in Appmon).
In Dynatrace you can build Oneagent plugins using python. You can execute shell script from the plugin python code, parse those values and return them as appropriate metrics. But there is no such plugin out-of-box. You will need to write yours.
Uhm, you are correct, this is for Dynatrace (not Appmon). I wasn't aware this exists. However, it seems this plugin sends the metrics to the Host entity. This is (at least it was) not enabled by default for tenants. So it depends on the Feature Flag value for you tenant whether you see the metrics or not.