Implement onurctirtir's suggestions

src/backend/distributed/metadata/node_metadata.c

@@ -1686,7 +1686,7 @@ citus_is_primary_node(PG_FUNCTION_ARGS)
 									"UDF. Otherwise, if you're going to use this node as a "
 									"worker node for a new cluster, make sure to add this "
 									"node into the metadata from the coordinator by using "
-                                    "citus_add_node() UDF."));
+									"citus_add_node() UDF.")));
 		PG_RETURN_NULL();
 	}
 

src/backend/distributed/sql/citus--12.1-1--12.2-1.sql

@@ -55,3 +55,4 @@ DROP VIEW IF EXISTS pg_catalog.citus_lock_waits;
 #include "udfs/citus_internal_update_relation_colocation/12.2-1.sql"
 #include "udfs/repl_origin_helper/12.2-1.sql"
 #include "udfs/citus_finish_pg_upgrade/12.2-1.sql"
+#include "udfs/citus_is_primary_node/12.2-1.sql"

src/backend/distributed/sql/downgrades/citus--12.2-1--12.1-1.sql

@@ -26,6 +26,7 @@ DROP FUNCTION citus_internal.commit_management_command_2pc();
 ALTER TABLE pg_catalog.pg_dist_transaction DROP COLUMN outer_xid;
 REVOKE USAGE ON SCHEMA citus_internal FROM PUBLIC;
 
+DROP FUNCTION pg_catalog.citus_is_primary_node();
 DROP FUNCTION citus_internal.add_colocation_metadata(int, int, int, regtype, oid);
 DROP FUNCTION citus_internal.add_object_metadata(text, text[], text[], integer, integer, boolean);
 DROP FUNCTION citus_internal.add_partition_metadata(regclass, "char", text, integer, "char");

src/backend/distributed/sql/udfs/citus_is_primary_node/12.2-1.sql

@@ -0,0 +1,7 @@
+CREATE FUNCTION pg_catalog.citus_is_primary_node()
+ RETURNS bool
+ LANGUAGE c
+ STRICT
+AS 'MODULE_PATHNAME', $$citus_is_primary_node$$;
+COMMENT ON FUNCTION pg_catalog.citus_is_primary_node()
+ IS 'returns whether the current node is the primary node in the group';