Add rf.request.setPathParams and rf.request.getPathParams to plugins

[zabojpetr]

Is possible to add getter and setter of path requests to plugins?

Usecase

When import requests from OpenAPI, there are a lot of path parameters which are not possible automatically fill with environment variable.
So I want to create plugin which automatically fill empty path parameters with environment variable with same name.

Originally posted by @zabojpetr in #317