fix: allow path_outputs to be outside of root dir

[mashb1t]

Fixes #907 and mashb1t#18

Allows Gradio to serve outputs when folder has been changed in the config.

See

• https://www.gradio.app/3.50.2/guides/sharing-your-app#security-and-file-access
• Gradio is unable to fetch a file from the specified path because it is not within the working directory of the Gradio app or it is not a temporary file created by the app. gradio-app/gradio#4118