Add database support

[aerni]

This PR adds support for storing Advanced SEO defaults in the database and closes #76.

Install the Statamic Eloquent Driver:

composer require statamic/eloquent-driver

Publish and run migrations:

php artisan vendor:publish --tag=statamic-eloquent-advanced-seo-migrations

php artisan migrate

Add this config to config/statamic/eloquent-driver.php

'advanced_seo' => [
    'driver' => 'eloquent',
    'model'  => Aerni\AdvancedSeo\Eloquent\SeoDefaultModel::class,
],

Import existing file-based Advanced SEO defaults into the database:

php please eloquent:import-advanced-seo

You may also export eloquent-based Advanced SEO defaults to flat files:

php please eloquent:export-advanced-seo

This installation process will be a lot easier once statamic/cms#11426 is merged. At that point, you can simply run php please install:eloquent-driver and follow the steps.

[lukevmk]

Would love to use this, when do you plan on merging this?

[aerni]

I'm still pondering on the best approach to configuring the eloquent driver, and wanted to wait on a decision in statamic/cms#11426 before merging. If this PR gets rejected, I might move the config into advanced-seo.php instead of eloquent-driver.php.