Issue #1919184 by nikhilasrani, vijaycs85: Create configuration schemas for menu module.

core/modules/menu/config/schema/menu.schema.yml

+# Schema for configuration files of the menu module.
+
+menu.settings:
+  type: mapping
+  label: 'Menu settings'
+  mapping:
+    main_links:
+      type: string
+      label: 'Main links'
+    secondary_links:
+      type: string
+      label: 'Source for secondary links'
+    override_parent_selector:
+      type: boolean
+      label: 'Override parent selector'
+
+menu.menu.*:
+  type: mapping
+  label: 'Menu'
+  mapping:
+    id:
+      type: string
+      label: 'Menu identifier'
+    label:
+      type: string
+      label: 'Menu label'
+    description:
+      type: text
+      label: 'Menu description'