Adding unity catalog skills

[lopesdiego12]

Summary

Adds databricks-unitycatalog, a Unity Catalog governance(parent: databricks-core). This skill focuses on discovering Unity Catalog objects, managing access, and operating UC-governed storage and observability.

Documentation safety checklist

• Discovery & inventory
  Navigate the 3-level namespace (catalog.schema.table), list catalogs/schemas/tables via CLI, and search metadata at scale using system.information_schema (tables, columns).

• Access control
  Grant, revoke, and troubleshoot permissions for catalogs, schemas, tables, views, volumes, and external locations. Covers key concepts such as BROWSE vs SELECT, USE CATALOG / USE SCHEMA traversal, and ownership vs MANAGE.

• Volumes & file governance
  Use UC managed and external volumes with canonical paths (/Volumes/<catalog>/<schema>/<volume>/...). Highlights the two-layer permission model for external volumes and the common requirement that WRITE FILES depends on READ FILES.

• Storage & connections
  Work with external locations, storage credentials, and governance patterns, including federation and data sharing concepts.

• Lineage & observability
  Understand lineage coverage, apply and audit tags, investigate actions via system.access.audit, and perform cost attribution using system.billing.usage.

• Operations & migration
  Perform maintenance (OPTIMIZE, VACUUM with retention and compliance considerations), use time travel, apply constraints, implement cloning strategies, and execute controlled Hive → UC migration workflows.

• AI/ML objects governance
  Apply governance principles to registered models, UC functions as controlled tools, vector search indexes, and feature workflows—avoiding embedding secrets in code.

[lopesdiego12]

@simonfaltum @lennartkats-db I don't know if I follow all the process to push that PR, can you please review that?