Add support for Atuin

[sbstn87]

I want to suggest a new step

https://github.com/atuinsh/atuin

Which tool is this about? Where is its repository?

Atuin replaces your existing shell history with a SQLite database, and records additional context for your commands. Additionally, it provides optional and fully encrypted synchronisation of your history between machines, via an Atuin server.

Which operating systems are supported by this tool?

Linux, MacOS

What should Topgrade do to figure out if the tool needs to be invoked?

Check if the app is installed

Which exact commands should Topgrade run?

atuin-update

Relevant thread:
atuinsh/atuin#2121