changefeedccl: json feed double escapes null byte in string

[asg0451]

Describe the problem

Please describe the issue you observed, and any steps we can take to reproduce it:

a json changefeed will double escape a null byte in a string as "\\x00" instead of "\u0000"

To Reproduce

create table stuff ( id string PRIMARY KEY,  data jsonb);
CREATE CHANGEFEED FOR TABLE stuff INTO '...'    WITH updated, resolved, format = json;
insert into stuff (id, data) values ('\000'::bytea::string, '{"a": 42}'::jsonb);

# observe the output in your sink of choice

Jira issue: CRDB-38376

[blathers-crl]

cc @cockroachdb/cdc