[Controls] Fix flaky apply button test (elastic#178661)

Closes elastic#178581

## Summary

Because the control group publishes its own filters to trigger unsaved
changes, and because the controls must **load** for the filters to be
published, we need to await for each control to load **before** saving
the dashboard - otherwise, if the controls fully load **after** the
dashboard is saved, this can re-trigger the unsaved changes badge.

### [Flaky Test
Runner](https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/5472)


![image](https://github.com/elastic/kibana/assets/8698078/271ecbca-9aee-43c1-83cf-54b4b7bf5a0d)


### Checklist

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [x] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed

### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

test/functional/apps/dashboard_elements/controls/common/control_group_apply_button.ts

@@ -24,8 +24,7 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
     'header',
   ]);
 
-  // FLAKY: https://github.com/elastic/kibana/issues/178581
-  describe.skip('Dashboard control group apply button', () => {
+  describe('Dashboard control group apply button', () => {
     let controlIds: string[];
 
     before(async () => {
@@ -51,7 +50,11 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
         title: 'Animal Name',
       });
       await dashboardControls.createTimeSliderControl();
+
+      // wait for all controls to finish loading before saving
       controlIds = await dashboardControls.getAllControlIds();
+      await dashboardControls.optionsListWaitForLoading(controlIds[0]);
+      await dashboardControls.rangeSliderWaitForLoading(controlIds[1]);
 
       // save the dashboard
       await dashboard.saveDashboard('Test Control Group Apply Button', { exitFromEditMode: false });