Use a context or variable for plugin_path in workflow.yaml

[dustinblack]

It's a pity that this line has to be changed and cannot be constructed from context (like line 13).

It would be cool if this entire file could be pulled from somewhere else with the custom bits filled in via inputs, context, or repository variables.

Originally posted by @webbnh in arcalot/arcaflow-plugin-coremark-pro#1 (comment)