fix: replace removed DBAL4 'json_array' type in install migration

[S-Tian86]

Why

A fresh oro:install on OroCommerce 7.0 aborts with:

ERROR: Unknown column type "json_array" requested. Any Doctrine type that you use has to be registered with \Doctrine\DBAL\Types\Type::addType().
> Synolia\Bundle\StockAlertBundle\Migrations\Schema\SynoliaStockAlertBundleInstaller

DBAL 4 (shipped with OroCommerce 7.0 / Symfony 7) removed the json_array column type (deprecated since DBAL 2.6, gone in DBAL 3). The installer still declared serialized_data as json_array, so the install aborts before synolia_stock_alert is created.

This was invisible to the oro:platform:update path (an existing migrated DB short-circuits getMigrationVersion() and never runs the table creation), so it only surfaces on a from-scratch install (CI / clean environments).

What

serialized_data now uses the native Types::JSON, which is the Oro 7.0 convention for the serialized-data column of extend entities. The stale legacy (DC2Type:array) comment and length => 0 are dropped accordingly.

-$table->addColumn('serialized_data', 'json_array', ['jsonb' => true, 'notnull' => false, 'length' => 0, 'comment' => '(DC2Type:array)']);
+$table->addColumn('serialized_data', Types::JSON, ['notnull' => false]);

Follow-up to the 7.0 migration (#15): this DBAL 4 break in the migration installer was missed there.

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