Defect #44454
openWebhook events list is empty after server start in development mode
Description
In development mode (`config.eager_load = false`), Rails lazy-loads model constants on demand via Zeitwerk. Webhook events are currently registered during the evaluation of model class definitions through the acts_as_webhookable macro (WebhookPayload.register_model(self, events)).
When starting the server in development mode and navigating directly to the webhooks configuration page (/admin/webhooks or /webhooks/new), the events checkbox list on the webhook creation/edit form is empty until the user first visits a page that loads those models (such as an issue or time entry page) - WebhookPayload.events returns an empty hash {}.
One way to fix this is to register these events in preparation.rb as we already do for activities or search.