EFTCLIENT-5390 Document /batch/close endpoint in Cloud API REST docs

[ecunado]

Add documentation for the batch close operation exposed via Cloud API.

Changes

• Introduce a “Batch Operations” section in restendpoints.md.
• Document POST /batch/close:
  • Usage and typical scenarios.
  • Parameters (ApiKeyCloud header + BatchCloseRequest body).
  • Return codes (200, 400, 422, 5xx) and behaviour notes.
  • Examples for a successful close and a validation error (missing batchNumber).
• Add Batch objects in restobjects.md:
  • BatchCloseRequest
  • BatchCloseResponse
• Cross-link endpoint and objects (restendpoints ↔ restobjects) for easier navigation.