Move empty_rule into components directory

The directory is currently like this:

• approvals/components/mr_edit/empty_rule.vue

But this component is also being used by project settings page. So instead it should be this:

• approvals/components/empty_rule.vue

This will make it match where the empty_rule_name.vue is. So the the steps would be:

1. move file outside of mr_edit
2. update references of this components
3. move tests to reflect this change