Improved completions for commands such as `asdf global <name> <version>` to list the installed versions
Added "complete asdf plugin versions installed" and "complete asdf plugin versions all" that produce completions for the installed versions and for all versions available for a given plugin
Improved `asdf install` completion to list the installed plugins and all the available versions
* Add test for nushell integration
* Add nushell to CI
* Fix brew installation search
* Fix to get current dir when ASDF_DIR is empty
* Remove complexity of asdf.nu
* Try a different approach to get info about function definition of asdf for MacOS 10.15
* Fix shims dir and fix test assertions to check path
* Add setup nushell to CI and remove rust compilation of nushell
* Add gh token to get a higher rate limit
* Change to use binary distribution of nushell instead compile it
* Skip test for older ubuntu
* Use single skipping check
* Remove unneeded condition in SKIP_NUSHELL_TESTS env var
