Environment variables from file in Actions

Having the possibility to define environment variables in the Actions is crucial in most situations, but it would be really nice to have the possibility to specify these variables from a file, so they can be reused across multiple actions without the need of replicate the list of env vars in each action.

It would be something like this:

---
name: "my_script"
runner_type: "remote-shell-cmd"
description: "Remote CMD with envs form file"
enabled: true
env_file: "/path/to/my/env/file"

Or as a parameter:

---
name: "my_script"
runner_type: "remote-shell-cmd"
description: "Remote CMD with envs form file"
enabled: true
parameters:
    env_file: 
       type: "string"
       default: "/path/to/my/env/file"

No implementation files or tests are named. Start by locating how StackStorm action YAML and action parameters are loaded, then trace the existing environment-variable handling; done means an action can load variables from the proposed env_file form and reuse them across actions with coverage for the supported configuration.