Add note to functions requiring superuser access (#967)

The following need superuser. Of them, the ones with arrows are present
in docs and are updated in this commit.

  	check_distributed_deadlocks
  	citus_blocking_pids
  	citus_isolation_test_session_is_blocked
->	master_activate_node
->	master_add_inactive_node
->	master_add_node
->	master_add_secondary_node
->	master_disable_node
->	master_remove_node
->	master_update_node
  	pg_catalog.citus_remote_connection_stats
  	pg_catalog.citus_stat_statements_reset
  	pg_catalog.coord_combine_agg
  	pg_catalog.coord_combine_agg_ffunc
  	pg_catalog.coord_combine_agg_sfunc
  	pg_catalog.master_drain_node
  	pg_catalog.master_set_node_property
  	pg_catalog.replicate_reference_tables
  	pg_catalog.worker_create_schema
  	pg_catalog.worker_partial_agg
  	pg_catalog.worker_partial_agg_ffunc
  	pg_catalog.worker_partial_agg_sfunc
  	pg_catalog.worker_record_sequence_dependency
  	pg_catalog.worker_repartition_cleanup
  	recover_prepared_transactions
  	worker_cleanup_job_schema_cache

develop/api_udf.rst

@@ -473,6 +473,10 @@ Metadata / Configuration Information
 master_add_node
 $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
 
+.. note::
+
+    This function requires database superuser access to run.
+
 The master_add_node() function registers a new node addition in the cluster in
 the Citus metadata table pg_dist_node. It also copies reference tables to the new node.
 
@@ -511,6 +515,10 @@ Example
 master_update_node
 $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
 
+.. note::
+
+    This function requires database superuser access to run.
+
 The master_update_node() function changes the hostname and port for a node registered in the Citus metadata table :ref:`pg_dist_node <pg_dist_node>`.
 
 Arguments
@@ -569,6 +577,10 @@ Example
 master_add_inactive_node
 $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
 
+.. note::
+
+    This function requires database superuser access to run.
+
 The :code:`master_add_inactive_node` function, similar to :ref:`master_add_node`,
 registers a new node in :code:`pg_dist_node`. However it marks the new
 node as inactive, meaning no shards will be placed there. Also it does
@@ -609,6 +621,10 @@ Example
 master_activate_node
 $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
 
+.. note::
+
+    This function requires database superuser access to run.
+
 The :code:`master_activate_node` function marks a node as active in the
 Citus metadata table :code:`pg_dist_node` and copies reference tables to
 the node. Useful for nodes added via :ref:`master_add_inactive_node`.
@@ -639,6 +655,10 @@ Example
 master_disable_node
 $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
 
+.. note::
+
+    This function requires database superuser access to run.
+
 The :code:`master_disable_node` function is the opposite of
 :code:`master_activate_node`. It marks a node as inactive in
 the Citus metadata table :code:`pg_dist_node`, removing it from
@@ -670,6 +690,10 @@ Example
 master_add_secondary_node
 $$$$$$$$$$$$$$$$$$$$$$$$$
 
+.. note::
+
+    This function requires database superuser access to run.
+
 The master_add_secondary_node() function registers a new secondary
 node in the cluster for an existing primary node. It updates the Citus
 metadata table pg_dist_node.
@@ -707,6 +731,10 @@ Example
 master_remove_node
 $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
 
+.. note::
+
+    This function requires database superuser access to run.
+
 The master_remove_node() function removes the specified node from the
 pg_dist_node metadata table. This function will error out if there
 are existing shard placements on this node. Thus, before using this