[SPIP 5] Revoir la compatibilité JS

En SPIP 5, le plugin a une erreur JS

Uncaught ReferenceError: onAjaxLoad is not defined
    <anonymous> https://dev.spip.test/plugins/zone/centre_image/centre_image_gestion.js?1767109342:196
    <anonymous> https://dev.spip.test/plugins/zone/centre_image/centre_image_gestion.js?1767109342:197

Memo: https://git.spip.net/spip/spip/-/blob/master/UPGRADE_5.0.md?ref_type=heads#fonctions-et-variables-javascript