Add migration guide and command

[JaZo]

Description

I added a migration guide and command to migrate to Laravel native encrypted casts.

Warning

This requires Laravel 12.18 as we rely on the functionality added by laravel/framework#55945. So I've bumped the minimum version and dropped support for Laravel 10 and 11.

Motivation and context

Closes #1.

How has this been tested?

Tested in a real application.

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have read the CONTRIBUTING document.
• My pull request addresses exactly one patch/feature.
• I have created a branch for this patch/feature.
• Each individual commit in the pull request is meaningful.
• I have added tests to cover my changes.
• If my change requires a change to the documentation, I have updated it accordingly.