Extension point: custom resource list rendering

[hpehl]

Parent: #320

Summary

Allow resources to customize how child resources are displayed in folder views. Currently, ResourceList renders each child with a generic name + stability label + View/Remove buttons, with no way to show resource-specific information or actions.

Motivation

• Custom list item rendering — show resource-specific info in each row (e.g., JNDI name for datasources, bound address:port for socket bindings, enabled/disabled badge for deployments, pool statistics)
• Custom actions per item — add resource-specific action buttons beyond View/Remove (e.g., "Enable", "Disable", "Test Connection", "Flush Pool", "Send Test Message")
• Custom toolbar actions — add buttons to the list toolbar beyond "Add" (e.g., bulk enable/disable, import/export, "Add from JDBC Driver")
• Custom empty state — resource-specific guidance when no children exist (e.g., "No datasources configured. Add a datasource to connect to a database." with a link to documentation)

Capabilities

• Custom item renderer — provide a function that adds extra content to each DataListItem based on the child's ModelNode data
• Custom action buttons — inject additional action buttons per item
• Custom toolbar — add toolbar items beyond the default filter + "Add" button
• Custom empty state — replace the default empty state with resource-specific content

Registration

A registry keyed by Environment + AddressTemplate. When ResourceList loads children for a matching template, the registry provides the rendering customizations.

Open Questions

• Should the custom renderer receive the full ModelNode of each child, or just the name? Loading full resources for the list could be expensive.
• How should custom actions interact with the existing onSelect/onAdd/onDelete callbacks?
• Should the list support different layout modes (e.g., card view vs list view) as an extension?