Finalization of generic endpoint and enhance/adjust current standardization documents

## Description

Finalizing the generic endpoint especially regarding business requirements.
Requirements aligned with architecture and datamodel team, if required
Requirements towards generic endpoint properly documented in confluence
Requirements towards dev properly described in respective dev tickets
Finalized generic endpoint description updated in BPDM Gate API Standard

## Impact

## Additional information

- [ ] I'm willing to contribute to this feature
- [x] https://github.com/eclipse-tractusx/bpdm/issues/382

Start by reviewing the requirements in the linked BPDM issue #382 and the existing BPDM Gate API Standard. Confirm alignment with the architecture and datamodel teams, then identify the relevant Confluence and development-ticket locations. Done means the generic endpoint requirements are documented, dev work is described in tickets, and the finalized endpoint description is reflected in the standard.

Written by the indexing model from the issue text.