config: add isolated option on the instance level

This commit just adds the option into the cluster configuration schema.
Next commits will add the relevant logic.

Part of tarantool#10796

NO_DOC=tarantool/doc#4632

Author: Totktonada

changelogs/unreleased/config-isolated-instance.md

@@ -0,0 +1,3 @@
+## feature/config
+
+* Add `isolated` option for instances (gh-10796).

src/box/lua/config/cluster_config.lua

@@ -202,7 +202,13 @@ local nested_cluster_config = schema.new(schema_name, record_from_fields({
                     instance_config_with_scope('replicaset'),
                     instances = schema.map({
                         key = name,
-                        value = instance_config_with_scope('instance'),
+                        value = record_from_fields({
+                            isolated = schema.scalar({
+                                type = 'boolean',
+                                default = false,
+                            }),
+                            instance_config_with_scope('instance'),
+                        }),
                     }),
                 }),
             }),

test/config-luatest/cluster_config_schema_test.lua

@@ -470,7 +470,11 @@ g.test_defaults = function()
 
     -- Instance defaults.
     --
-    -- There are no additional options.
+    -- There is an additional option:
+    --
+    -- * isolated (default: false)
+    local exp = table.copy(exp)
+    exp.isolated = false
     local res = cluster_config:apply_default({
         groups = {
             g = {
@@ -729,13 +733,37 @@ end
 
 -- Verify options consistency on the instance level.
 --
--- Expected only instance config fields.
+-- Expected instance config fields plus the following additional
+-- ones:
+--
+-- * isolated (boolean)
 g.test_additional_options_instance = function()
+    -- Some valid values for the additional fields.
+    local additional_options = {
+        isolated = true,
+    }
+
     -- Verify that the fields on the given level are instance
-    -- config fields.
+    -- config fields plus the given additional ones.
     local schema = cluster_config.schema
         .fields.groups.value
         .fields.replicasets.value
         .fields.instances.value
-    verify_fields(schema, {})
+    verify_fields(schema, table_keys(additional_options))
+
+    -- Verify that the given example values for the additional
+    -- fields are accepted by the schema on the given level.
+    cluster_config:validate({
+        groups = {
+            g = {
+                replicasets = {
+                    r = {
+                        instances = {
+                            i = additional_options,
+                        },
+                    },
+                },
+            },
+        },
+    })
 end