[10.x] Enhancement of Interface Cloud: Addition of fileExists method

[BadJacky]

Description:
This pull request addresses a recurring PHPStan error that point out an undefined method, fileExists(), being called on the Illuminate\Contracts\Filesystem\Cloud interface.

This has been corrected by introducing a fileExists() method in the Cloud interface, which clarifies the contract for all classes that implement this interface. Consequently, it serves two essential tasks:

Fixes PHPStan error: Call to an undefined method Illuminate\Contracts\Filesystem\Cloud::fileExists(). when I using the Storage::cloud()->fileExists($s3_relative_path) to ensure the determine if a file exists.
Makes the interface's responsibilities more explicit and precise.
Modified Files:
Illuminate\Contracts\Filesystem\Cloud
Tasks:
Add fileExists() method to the Cloud interface
Update all the classes that implement Cloud interface and provide an implementation for fileExists()
Testing:
After the correction:

All existing tests should pass without any error
No PHPStan errors should be thrown for Call to an undefined method Illuminate\Contracts\Filesystem\Cloud::fileExists(). ✏️ app/Console/Commands/File/Retrieve.php
Note: This PR doesn't include implementations for fileExists(). The classes that implement Cloud should provide their own.

[GrahamCampbell]

This is a breaking change, and cannot be made on the 10.x series.

[BadJacky]

@GrahamCampbell
Is not this a BC ?
#47664

[GrahamCampbell]

No, that is a bug fix. All bug fixes could be argued to be BC breaks... but the difference is that a bug fix is changing to something to what it was always meant to be. This PR does not do that.