FIX: ensures group automatic membership dropdown works (#9022)

This commit also fixes a deprecation warning as the previous  component was overriding a computed property from the group model.

Finally a test has been added as this is the only place where we use list-setting outside of the settings, this was highly subject to regressions.

test/javascripts/acceptance/group-manage-membership-test.js.es6

@@ -1,4 +1,5 @@
 import { acceptance, updateCurrentUser } from "helpers/qunit-helpers";
+import selectKit from "helpers/select-kit-helper";
 
 acceptance("Managing Group Membership", {
   loggedIn: true
@@ -65,6 +66,13 @@ QUnit.test("As an admin", async assert => {
     1,
     "it should display the membership request template field"
   );
+
+  const emailDomains = selectKit(".group-form-automatic-membership-automatic");
+  await emailDomains.expand();
+  await emailDomains.fillInFilter("foo.com");
+  await emailDomains.keyboard("enter");
+
+  assert.equal(emailDomains.header().value(), "foo.com");
 });
 
 QUnit.test("As a group owner", async assert => {