[Feature]: `cargo shuttle upgrade`

[jonaro00]

Describe the feature

Add a command that runs either curl -sSfL https://www.shuttle.rs/install | bash with bash or iwr https://www.shuttle.rs/install-win | iex with powershell based on which platform cargo-shuttle was compiled on

Suggestion or Example of how the feature would be used

Just a convenience over having to look up the installer command every time. In the future, this command could also help with bumping dependencies, etc.

Duplicate declaration

• [X] I have searched the issues and this feature has not been requested before.

[supleed2]

I'd like to take a shot at this one :)