changefeedccl: allow users to alter the sink URI of an existing changefeed

[cockroach-teamcity]

Exalate commented:

cockroachdb/cockroach#77043 --- Release note (enterprise change): Users may now alter the sink URI of an existing changefeed. This can be achieved by executing the following statement: ALTER CHANGEFEED <job_id> SET sink = '<sink_uri>' Where the sink type of the new sink must match the sink type of the old sink that was chosen at the creation of the changefeed.

Jira Issue: DOC-2753