request: Make explicit upgrade command

[erf]

Is there an existing feature request for this?

• [X] I have searched the existing issues.

Command

flutterfire upgrade

Description

Add a flutterfire upgrade command which upgrades the tool to the latest version (if available).

Reasoning

I was wondering how to update the flutterfire CLI tool and noticed a upgrade prompt after typing flutterffire version, maybe there could be an explicit command for this.

Additional context and comments

No response