Draft: Changes for gRPC CTA Frontend

Add some comments

Checkout version 1.16 on the xrootd-ssi submodule

This is required in order to have the grpc methods in cta_frontend

Start adding a new client class

Add some gRPC calls in the appropriate place, obviously this doesn't work yet

Put the grpc call into a function

(Could be useless)

Update includes in WFE.cc

Update CMakeLists.txt in common/eos_cta_pb

Fix CreateChannel call

More fixes