Merged pull request https://github.com/scylladb/scylla/pull/5538 from
Avi Kivity and Piotr Jastrzębski.
This series prepares CDC for rolling upgrade. This consists of
reducing the footprint of cdc, when disabled, on the schema, adding
a cluster feature, and redacting the cdc column when transferring
it to other nodes. The latter is needed because we'll want to backport
this to 3.2, which doesn't have canonical_mutations yet.
Fixes#5191.
(cherry picked from commit f0d8dd4094)
edf431f581