Extension point: custom tabs

[hpehl]

Parent: #320

Summary

Allow resources to contribute additional tabs to ResourceTabs, or replace/remove default tabs. Currently, ResourceTabs hardcodes four tabs (Data, Attributes, Operations, Capabilities) with no way for consumers to customize them.

Motivation

The /subsystem=elytron/credential-store=* resource would benefit from an "Aliases" tab alongside the default tabs. Similar use cases exist for other resources that have domain-specific data that doesn't fit into the generic attribute view (e.g., deployments content, messaging queues, datasource connection pools).

Capabilities

• Add tabs — inject extra tabs after the "Data" tab (or at a specified position)
• Remove tabs — suppress default tabs that aren't useful for a resource (e.g., hide "Capabilities" when empty)
• Replace tab content — swap the content of an existing tab with a custom implementation

Registration

A registry keyed by Environment + AddressTemplate. When ResourceTabs is constructed for a matching template, the registry provides the tab customizations.

Open Questions

• Should custom tabs receive the same Metadata and loaded ModelNode that the Data tab uses, or should they load their own data?
• How should tab ordering work when multiple extensions match (e.g., a wildcard and an exact template)?
• Should there be a standard interface/abstract class for custom tab content?