3454592 : provide a disable modal option

Closes #3454592

config/schema/simple_terms_and_menus.schema.yml

+simple_terms_and_menus.settings:
+  type: config_object
+  mapping:
+    disable_menu_modal:
+      label: 'Disable menu modal'
+      type: boolean
+    disable_term_modal:
+      label: 'Disable term modal'
+      type: boolean
+    disable_media_modal:
+      label: 'Disable media modal'
+      type: boolean