restrict openapi spec based on sql grants

test/spec/fixtures/privileges.sql

@@ -28,10 +28,13 @@ REVOKE ALL PRIVILEGES ON TABLE
     , authors_only
     , insertonly
     , limited_article_stars
+    , selectonly
 FROM postgrest_test_anonymous;
 
 GRANT INSERT ON TABLE insertonly TO postgrest_test_anonymous;
 
+GRANT SELECT ON TABLE selectonly TO postgrest_test_anonymous;
+
 GRANT USAGE ON SEQUENCE
       auto_incrementing_pk_id_seq
     , items_id_seq

test/spec/fixtures/schema.sql

@@ -1926,6 +1926,11 @@ create table app_users (
   password text       not null
 );
 
+create table selectonly (
+  id   integer primary key,
+  name text
+);
+
 create table private.pages (
   link int not null unique
 , url text