mgr/dashboard: refactor /api/orchestrator/* endpoints

mgr/dashboard: refactor /api/orchestrator/* endpoints

- API changes:
  - Move `/api/orchestrator/identify_device` to
    `/api/host/<hostname>/identify_device`.
  - Move `/api/orchestartor/inventory` to `/ui-api/host/inventory`. This
    UI API provides a shortcut to get all inventories.
  - Add `/api/host/<hostname>/inventory` for getting a host's inventory.
  - Add inventory schema to improve OpenAPI doc.
- Backend unittests:
  - Refactor: Remove duplicated orchestrator patch calls.
  - Add unittest for identify device.

Fixes: https://tracker.ceph.com/issues/43165
Signed-off-by: Kiefer Chang <kiefer.chang@suse.com>