Replicate Postgres to Cockroach
CockroachDB PM here. I don't have a very satisfying answer for you, unfortunately; Postgres logical decoding is difficult to implement correctly, and I don't know of anything offhand that satisfies your needs.

Postgres links to a number of off-the-shelf logical decoding plugins, but in my experience these are of varying quality. If you use one of these, you'll want to verify that it properly handles columns that use Postgres's TOAST mechanism -- last time I looked at these, they generally did not. After you get your data streaming out of Postgres, you can consume them and upsert them into your Cockroach database on a separate SQL connection.

If a zero-downtime migration is not required, you could use CockroachDB's IMPORT PGDUMP functionality: use Postgres's own dump functionality to dump your data to a file, and then import it into CockroachDB.