In the future commit, we change how we initialize uuid of the
new CDC generation in the Raft-based topology. It forces us to
move this initialization out of the make_new_generation_data
function shared between Raft-based and gossiper-based topologies.
We also rename make_new_generation_data to
make_new_generation_description since it only returns
cdc::topology_description now.
3bf4cac72e