Update lua_call config description

Author: p7nov

doc/code_snippets/snippets/replication/instances.enabled/supervised_failover/source.yaml

@@ -5,7 +5,7 @@ credentials:
       roles: [ replication ]
       privileges:
       - permissions: [ execute ]
-        functions: [ 'failover.execute' ]
+        lua_call: [ 'failover.execute' ]
 
 iproto:
   advertise:
@@ -23,8 +23,6 @@ failover:
     keepalive_interval: 5
     renew_interval: 1
 
-roles: [ 'supervised_instance' ]
-
 groups:
   group001:
     replicasets:

doc/code_snippets/snippets/replication/instances.enabled/supervised_failover/supervised_instance.lua

@@ -124,21 +124,6 @@ To configure a cluster to work with an external failover coordinator, follow the
         :end-at: failover.execute
         :dedent:
 
-4.  Create the ``failover.execute`` function in the application code.
-    For example, you can create a :ref:`custom role <application_roles>` for this purpose:
-
-    ..  literalinclude:: /code_snippets/snippets/replication/instances.enabled/supervised_failover/supervised_instance.lua
-        :language: lua
-        :dedent:
-
-    Then, you need to enable this role for all storage instances:
-
-    ..  literalinclude:: /code_snippets/snippets/replication/instances.enabled/supervised_failover/source.yaml
-        :language: yaml
-        :start-at: supervised_instance
-        :end-before: groups:
-        :dedent:
-
 5.  (Optional) Configure options that control how a failover coordinator operates in the :ref:`failover <configuration_reference_failover>` section:
 
     ..  literalinclude:: /code_snippets/snippets/replication/instances.enabled/supervised_failover/source.yaml

doc/platform/replication/supervised_failover.rst

@@ -1445,7 +1445,8 @@ credentials.users.*
 
 .. confval:: <user_or_role_name>.privileges.lua_call
 
-    Whether this user or a user with this role can call any global user-defined Lua function.
+    A list of global user-defined Lua functions that this user or a user with this role can call.
+    To allow calling all such functions, specify the ``all`` value.
 
 ..  _configuration_reference_credentials_privileges_sql: