[12.x] Add UUID v7 section for Models to upgrade guide

[HasanQQ]

With laravel 12, the HasUuids trait using v7 UUIDs by default. If we compare the examples below, the order of the database records may become confusing.

Str::orderedUuid()
Ramsey\Uuid\Rfc4122\UuidV4 {#5343
  uuid: "9e4bb9bd-f73d-41c2-aecf-8c9bf81eb188",
}

Str::uuid7()
Ramsey\Uuid\Lazy\LazyUuidFromString {#5295
  uuid: "01953cbc-ceac-73a4-9829-a14fc6528306",
}

I'm not sure about my writing style, but I think there should be such a section in the upgrade documentation.

[nshiro]

We should also mention that the HasVersion7Uuids trait was removed in Laravel 12.
If you are using it, you should migrate to the HasUuids trait.
laravel/framework#52433