Decouple version save logic into separate method

[mirzazeyrek]

Thank you for the great work on the package!

I have integrated into an existing project and noticed a functionality we need was missing. So introducing saveVersion model for forcing to create a version without any changes.

Example use case through a migration:

<?php

use App\Models\CustomerDocument;
use Illuminate\Database\Migrations\Migration;

class CreateVersionsForDocuments extends Migration
{
    public const REASON = 'MIGRATION';

    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        $customerDocuments = CustomerDocument::all();
        foreach($customerDocuments as $customerDocument) {
            if(!$customerDocument->currentVersion()) {
                $customerDocument->setReasonAttribute(self::REASON);
                $customerDocument->saveVersion();
            }
        }
    }