Add Laravel Cashier 13 & 14 upgrade rules

[GeniJaho]

Relates to #100

This PR introduces initial support for upgrading Laravel Cashier to version 13 and 14.

It only handles the method renames, since other upgrades are out of the scope (and capability) of Rector.

[GeniJaho]

Should I include the LaravelCashierSetList class somewhere? The CI fails since the class is currently unused in the project.

[driftingly]

@GeniJaho What do you think of having config/sets/packages/cashier-13.php?
If other package-specific sets are developed we could group them there?

[GeniJaho]

Yes, that would be a lot better. Any idea to make the failing check to pass? The CashierSetList class is not used anywhere.

[driftingly]

@GeniJaho sorry, that was my suggestion for the set list. Having something like what you did for Laravel 10:
https://github.com/driftingly/rector-laravel/blob/main/config/sets/level/up-to-laravel-100.php

[driftingly]

@GeniJaho is this ready?
If it's ready to go can you merge in main and update the docs?
Thanks!

[GeniJaho]

@driftingly this is ready now, I updated the docs and main was merged. Not sure why that test failed before the merge though, I couldn't make it fail locally.