config: snapshot section for instance config

This section describes the instance snapshot configuration.

Part of #8778

NO_DOC=will be added later
NO_CHANGELOG=will be added later

src/box/lua/config/instance_config.lua

@@ -453,6 +453,37 @@ return schema.new('instance_config', schema.record({
             default = 4 * 3600,
         }),
     }),
+    snapshot = schema.record({
+        dir = schema.scalar({
+            type = 'string',
+            box_cfg = 'memtx_dir',
+            box_cfg_nondynamic = true,
+            mkdir = true,
+            default = '{{ instance_name }}',
+        }),
+        by = schema.record({
+            interval = schema.scalar({
+                type = 'number',
+                box_cfg = 'checkpoint_interval',
+                default = 3600,
+            }),
+            wal_size = schema.scalar({
+                type = 'integer',
+                box_cfg = 'checkpoint_wal_threshold',
+                default = 1e18,
+            }),
+        }),
+        count = schema.scalar({
+            type = 'integer',
+            box_cfg = 'checkpoint_count',
+            default = 2,
+        }),
+        snap_io_rate_limit = schema.scalar({
+            type = 'number',
+            box_cfg = 'snap_io_rate_limit',
+            default = box.NULL,
+        }),
+    }),
 }, {
     -- Any configuration data should contain a version of the
     -- config schema for which it is written.

test/config-luatest/instance_config_schema_test.lua

@@ -352,3 +352,31 @@ g.test_wal = function()
     local res = instance_config:apply_default({}).wal
     t.assert_equals(res, exp)
 end
+
+g.test_snapshot = function()
+    local iconfig = {
+        snapshot = {
+            dir = 'one',
+            by = {
+                interval = 1,
+                wal_size = 1,
+            },
+            count = 1,
+            snap_io_rate_limit = 1,
+        },
+    }
+    instance_config:validate(iconfig)
+    validate_fields(iconfig.snapshot, instance_config.schema.fields.snapshot)
+
+    local exp = {
+        dir = '{{ instance_name }}',
+        by = {
+            interval = 3600,
+            wal_size = 1000000000000000000,
+        },
+        count = 2,
+        snap_io_rate_limit = box.NULL,
+    }
+    local res = instance_config:apply_default({}).snapshot
+    t.assert_equals(res, exp)
+end