Add "run-script" feature

[sebst]

Feature should get a url or a multiline script via options.

If a url is provided, the url should be temporarily downloaded via wget or curl (if one of those are installed) OR via curl (if that needs to be installed).

If a text script is provided, the text should be stored in a temporary script file.

If both are provided, the feature should fail to install.

Finally, the temporary script should be executed.