Clean-up string usage

[marthtz]

Brief feature description

Iceoryx uses a variety of strings (std::string, cxx::string<>, cxx::CString100, etc).
Once #253 is merged this mishmash should be cleaned-up.

Detailed information

Only use cxx:string<> or types created from it.

• No std::string in public API

• No more std::strings in code base

  • iceoryx_hoofs
    • Taken from: Enable clang-tidy checks and fix warnings in code #1196 Refactor cxx::convert so that all cxx::string capacities are handled
  • iceoryx_posh
  • iceoryx_dds

• No more CSring100 in code base

• Common convention for string aliases. Currently we have:

  • alias without _t, e.g. IdString
  • alias with _t, e.g. ProcessName_t
  • alias nested in a class, e.g. PosixUser::string_t
  • alias with a constexpr as string length, e.g. cxx::string<MAX_LENGTH>
  • alias without a constexpr as string length, e.g. cxx::string<100>
  • see also https://github.com/eclipse/iceoryx/pull/373/files#r525922015 and https://github.com/eclipse/iceoryx/pull/373/files#r525922656
  • cleanup iceoryx_hoofs
  • cleanup iceoryx_posh
  • cleanup iceoryx_dds

[FerdinandSpitzschnueffler]

I will work on it