[Discussion] Support CppClient in Celeborn

[Jiaming Xie]

Hi all,
    I wrote a CIP about supporting CppClient in Celeborn, and the CIP draft
is
https://docs.google.com/document/d/1EMx1fryZx0gKd4Q32uQEi1835kNhB92yRjteILQpijg/edit?usp=sharing
 .
    Any suggestion is welcome. Let's make Celeborn better together.
Jiaming Xie