Update documentation for Schema Isolation, Views

[chikaj]

PostgreSQL 15 introduced security_invoker that can be called on CREATE VIEW. The situation described under the PostgREST documentation "Schema Isolation, View" is still relevant, but now rather than making a non-superuser the view's owner, you can now CREATE OR REPLACE VIEW my_view WITH (security_invoker=true) AS ... and RLS on the base table will be honored.

[chikaj]

My mistake. Found it already in the issues.

#589