Adds GRANT for public to citus_tables

(cherry picked from commit 5c5cb200f7)

src/backend/distributed/sql/citus--10.0-1--10.0-2.sql

@@ -1,3 +1,5 @@
 -- citus--10.0-1--10.0-2
 
 #include "../../columnar/sql/columnar--10.0-1--10.0-2.sql"
+
+GRANT SELECT ON public.citus_tables TO public;

src/backend/distributed/sql/downgrades/citus--10.0-2--10.0-1.sql

@@ -1,2 +1,4 @@
 /* citus--10.0-2--10.0-1.sql */
 #include "../../../columnar/sql/downgrades/columnar--10.0-2--10.0-1.sql"
+
+REVOKE SELECT ON public.citus_tables FROM public;

src/test/regress/expected/multi_multiuser.out

@@ -287,6 +287,13 @@ ERROR:  permission denied for table stripe
 -- (since citus extension has a dependency to it)
 DROP TABLE columnar.chunk;
 ERROR:  must be owner of table chunk
+-- test whether a read-only user can read from citus_tables view
+SELECT distribution_column FROM citus_tables WHERE table_name = 'test'::regclass;
+ distribution_column
+---------------------------------------------------------------------
+ id
+(1 row)
+
 -- check no permission
 SET ROLE no_access;
 EXECUTE prepare_insert(1);

src/test/regress/sql/multi_multiuser.sql

@@ -184,6 +184,11 @@ INSERT INTO columnar.stripe VALUES(99);
 -- (since citus extension has a dependency to it)
 DROP TABLE columnar.chunk;
 
+
+-- test whether a read-only user can read from citus_tables view
+SELECT distribution_column FROM citus_tables WHERE table_name = 'test'::regclass;
+
+
 -- check no permission
 SET ROLE no_access;