Add an easy way to install for linux users

[TanZng]

What would you like to be added? Create a asdf-plugin to install spotctl throw asdf.

Why is this needed? brew is nice but is only macOS users, for Linux users spotctl is not so easy to install, that's why I propose create a way to install spotctl with asdf. Other CLI projects already do this and is very helpful to install and manage the cli versions.

Examples: https://github.com/asdf-community/asdf-kubectl https://github.com/kforsthoevel/asdf-goreleaser