[frontend] Creates new Namespace object to hold EOS ns config

xroot_plugins/CMakeLists.txt

xroot_plugins/GrpcEndpoint.cpp

xroot_plugins/GrpcEndpoint.hpp

xroot_plugins/Namespace.hpp

xroot_plugins/XrdCtaTapeFileLs.hpp

xroot_plugins/XrdSsiCtaRequestMessage.cpp

xroot_plugins/XrdSsiCtaRequestMessage.hpp

xroot_plugins/XrdSsiCtaServiceProvider.cpp

xroot_plugins/XrdSsiCtaServiceProvider.hpp