[BYO-S3] Warehouse REST endpoints + Lakekeeper client + per-execution injection

[mengw15]

Task Summary

Part of #6870. The backend that lets a user manage warehouses and pick one for a run. Everything
here is gated by warehousesEnabled, so it stays invisible while the flag is off.

• Warehouse management API — REST endpoints on the central web service (WarehouseResource,
  registered in TexeraWebApplication): list your warehouses + the flag state
  (GET /warehouse/status), create one (POST /warehouse, Local/MinIO flavor here), delete one
  (DELETE /warehouse/{whid}). Guards return 403 when the flag is off.
• Lakekeeper management client — a new LakekeeperClient that creates the warehouse via
  Lakekeeper's management API, and deletes it empty-first (Lakekeeper refuses to drop a
  non-empty warehouse): drop each table with purgeRequested=false → drop namespaces → delete the
  warehouse, so the S3 data files are kept.
• Per-execution warehouse resolution — WorkflowService.resolveWarehouseName(whid, uid) maps
  the chosen whid to its warehouse name, checks the requesting user owns it, and injects it into
  the run's WorkflowContext — only when warehousesEnabled; otherwise runs use the shared
  default warehouse exactly as today.

Task Type

• Other (feature implementation)