document how to activate a new version of postgres-singer-io tap schema - `key_properties` change detected

[michaelklotz]

After updating a singer.io target-postgres tap to use a new key, I see the following error:

 target_postgres.exceptions.PostgresError: ('Exception writing records', PostgresError("`key_properties` change detected. Existing values are: ['uri']. Streamed values are: ['id']"))
[2022-10-20, 19:22:01 UTC] {{taskinstance.py:1902}} ERROR - Task failed with exception

the target table comment is configured like this....

comment on table redacted.redacted is '{"path": ["redacted"], "version": 1, "schema_version": 3, "key_properties": ["uri"] ....

it used to have "key_properties": ["id"].

This functionality is listed as a feature, but there is no documentation on how to use it.