Left-over from cxx::list implementation

## Brief feature description
Following points were discussed by are shifted herewith to a new issue
- [ ] consider using cxx::optional / cxx::expected in return values (possibly w/ stl-conform wrapper)
- [x] addressed via #260 ~~replace magic numbers like cxx::string<100> e.g. in port handling context (discuss naming type concept for port management)~~
- [ ] interface between port_manager and port_pool shall be drawn clearer. E.g. port_manager shall not (directly) work with port pool container (list).
- [x] addressed via #130 ~~handling for misuse detection in cxx::forward::list, cxx::list (usage of invalid iterators (invalid element or wrong list))~~

## Detailed information

E.g. a list of pros and cons of different considerations and how iceoryx and its user could benefit from it