[IMP] base_import: defer parent store

Makes possible to choose `defer_parent_store_computation` in UI.

Closes #21320

addons/base_import/static/src/js/import_action.js

@@ -316,6 +316,7 @@ var DataImport = Widget.extend(ControlPanelMixin, {
         this.$('.oe_import_float_decimal_separator').val(result.options.float_decimal_separator).change();
         if (result.debug === false){
             this.$('.oe_import_tracking').hide();
+            this.$('.oe_import_deferparentstore').hide();
         }
 
         var $fields = this.$('.oe_import_fields input');
@@ -454,10 +455,12 @@ var DataImport = Widget.extend(ControlPanelMixin, {
             return $(el).select2('val') || false;
         }).get();
         var tracking_disable = 'tracking_disable' in kwargs ? kwargs.tracking_disable : !this.$('#oe_import_tracking').prop('checked')
+        var defer_parent_store = 'defer_parent_store' in kwargs ? kwargs.defer_parent_store : !!this.$('#oe_import_deferparentstore').prop('checked')
         delete kwargs.tracking_disable;
+        delete kwargs.defer_parent_store;
         kwargs.context = _.extend(
             {}, this.parent_context,
-            {tracking_disable: tracking_disable}
+            {tracking_disable: tracking_disable, defer_parent_store_computation: defer_parent_store}
         );
         return this._rpc({
                 model: 'base_import.import',

addons/base_import/static/src/xml/base_import.xml

@@ -63,6 +63,15 @@
                         Track history during import
                     </label>
                 </div>
+                <div title="If the model uses parent/child relations, computing the 
+                    parent / child relation occurs on every line, and lead to a slower import.
+                    Defering it can speed up import."
+                    class="oe_import_deferparentstore">
+                    <input type="checkbox" id="oe_import_deferparentstore" checked="checked"/>
+                    <label for="oe_import_deferparentstore">
+                        Defer parent/child computation
+                    </label>
+                </div>
                 <input type="checkbox" class="oe_import_has_header"
                        id="oe_import_has_header" checked="checked"/>
                 <label for="oe_import_has_header">The first row