doc: Clarify logical replication documentation

Document that the data types of replicated tables do not need to
match.  The documentation previously claimed that they had to match.

Author: Robert Treat <rob@xzilla.net>
Discussion: https://www.postgresql.org/message-id/flat/CAJSLCQ13==D8Ka2YLyctTm0Y+8MhGYcX_zj7fU0rqRzhcV++3w@mail.gmail.com