Please explain in the README how to use the external copilot-language-server

copilot.vim bundles it, but some people don't like bundling and would like to use standalone copilot-language-server package.
[Repology](https://repology.org/projects/?search=copilot-language-server) shows that NixOS already has such package, and I am also going to create one for FreeBSD.

Is there an easy way to switch between the bundled copilot-language-server and external copilot-language-server ?

Command or setting that can switch it persistently?