@budibase/server: Unauthenticated webhook schema update vulnerability

The webhook schema-building endpoint at POST /api/webhooks/schema/:instance/:id is incorrectly bypassed by authorization middleware, allowing unauthenticated users to update webhook body schemas and automation trigger output schemas.

All Budibase instances with webhook-backed automations; any unauthenticated attacker with a known webhook ID can modify schema data.

Apply the fix by removing the schema path from the WEBHOOK_ENDPOINTS regex or adding explicit authorization checks for the schema-building endpoint.